Polymer-inorganic particle composites

ABSTRACT

Inorganic particle/polymer composites are described that involve chemical bonding between the elements of the composite. In some embodiments, the composite composition includes a polymer having side groups chemically bonded to inorganic particles. Furthermore, the composite composition can include chemically bonded inorganic particles and ordered copolymers. Various electrical optical and electro-optical devices can be formed from the composites.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of copending U.S. patent applicationSer. No. 10/422,149, now U.S. Pat. No. ______to Kambe et al., filed onApr. 24, 2003, entitled “Polymer-Inorganic Particle Composites,”incorporated herein by reference, which is a divisional of U.S. patentapplication Ser. No. 09/818,141, now U.S. Pat. No. 6,599,631 to Kambe etal., filed on Mar. 27, 2001, entitled “Polymer-Inorganic ParticleComposites,” incorporated herein by reference, which claims priority toU.S. Provisional Application Ser. No. 60/265,169 filed on Jan. 26, 2001,entitled “Polymer-Inorganic Particle Composites,” incorporated herein byreference.

BACKGROUND OF THE INVENTION

The invention relates to composites combining inorganic particles andpolymers. The invention further relates to inorganic particles that arefunctionalized for chemical bonding to other compounds, particularly topolymers.

Advances in a variety of fields have created a demand for many types ofnew materials. In particular, a variety of chemical powders can be usedin many different processing contexts. Specifically, inorganic powderscan be used in the production of electronic devices, such as flat paneldisplays, electronic circuits and optical and electro-optical materials.

Similarly, technological advances have increased the demand for improvedmaterial processing with strict tolerances on processing parameters. Asminiaturization continues even further, material parameters will need tofall within stricter tolerances. Current integrated circuit technologyalready requires tolerances on processing dimensions on a submicronscale. Self-assembly approaches have been developed to provideadditional options for the application of very thin films of materials.However, self-assembly approaches generally have been limited withrespect to the types of materials that can be deposited by a particularapproach.

The consolidation or integration of mechanical, electrical and opticalcomponents into integral devices has created further demands on materialprocessing. Therefore, there is considerable interest in the formationof specific compositions applied to substrates to perform specificfunctions. In order to form optical devices with high quality opticalcoatings from these materials, the coatings must be highly uniform.

Composite materials can be used to combine desirable properties ofdifferent materials to obtain improved materials. Alternatively,composite materials can be formed to capture improved or more flexibleprocessing capabilities associated with one material with desirableproperties of another material. Thus, in the composite materials,desirable properties of one material can be incorporated into a widerrange of structures based on the processing capabilities enabled byanother component of the composite. For composites to be useful incertain applications the composites must be structurally stable.

SUMMARY OF THE INVENTION

In a first aspect, the invention pertains to a composite compositioncomprising a polymer having side groups, chemically-bonded to inorganicparticles. Polymers broadly include oligomers.

In another aspect, the invention pertains to a composite compositioncomprising inorganic particles chemically bonded to a polymer through alinkage comprising a plurality of functional groups, the polymerselected from the group consisting of polyamides, polycarbonates,polyimides, polyphosphazenes, polyurethanes, polyacrylates,polyacrylamides, heterocyclic polymers, polysiloxanes,polyacrylonitrile, polyacrylic acid, polyvinyl alcohol, polyvinylchloride, conjugated polymers, aromatic polymers, electricallyconducting polymers and mixtures thereof The polymers possess functionalside groups and/or terminal sites that can be chemically bonded with theinorganic particles, which generally are functionalized by bonding witha linker compound.

Also, the invention pertains to a composite composition comprisingchemically bonded inorganic particles and polymer selected from thegroup consisting of polyamides, polycarbonates, polyimides,polyphosphazenes, polyurethanes, heterocyclic polymers, polysiloxanes,polyacrylonitrile, polyacrylic acid, polyvinyl alcohol, polyvinylchloride, conjugated polymers, aromatic polymers, electricallyconducting polymers and mixtures thereof. The polymer is chemicallybonded to the inorganic particle at a terminal site of a polymer chain.

In a further aspect, the invention pertains to a composite compositioncomprising a polymer chemically bonded to inorganic particles, whereinthe inorganic particles comprise a metal.

In addition, the invention pertains to a collection of metal/metalloidoxide or metal/metalloid nitride particles that are chemically bondedthrough a chemical linkage comprising an amine group, an amide group, asulfide group, a disulfide group, an alkoxy group, a ester group, anacid anhydride group. The linkage is chemically bonded with a polymer.

Furthermore, the invention pertains to a composite compositioncomprising chemically bonded inorganic particles and blends of distinctpolymers.

In additional aspects, the invention pertains to a structure comprisinga surface and a composite localized within boundaries on the surface.The composite comprises inorganic particles bonded to a polymer.

In other aspects, the invention pertains to a method for formingchemically bonded polymer inorganic particle composites. The methodcomprises binding side chain functional groups of polymer units tofunctional groups of a linker compound bonded to the inorganicparticles.

In additional aspects, the invention pertains to an optical devicecomprising a composite. The composite comprises a polymer and inorganicparticles chemically bonded to the polymer.

In further aspects, the invention pertains to a method for forming adevice on a solid substrate. The method comprises associating acomposite with the solid substrate. The composite comprises a polymerchemically bonded with an inorganic particle.

BRIEF DESCRIPTION OT THE DRAWINGS

FIG. 1 is a schematic diagram of an embodiment of a polymer/inorganicparticle composite.

FIG. 2 is a schematic diagram of an alternative embodiment of apolymer/inorganic particle composite with a low degree of crosslinkednetwork.

FIG. 3 is a schematic diagram depicting an inorganic particles bonded toa plurality of linkers to form a star linkage in a composite.

FIG. 4 is a schematic diagram of another alternative embodiment of apolymer/inorganic particle composite with a high degree of crosslinking.

FIG. 5 is a schematic diagram of an embodiment of a polymer/inorganicparticle composite with particles tethered to a polymer chain.

FIG. 6 is a schematic diagram of a copolymer with partial tetheredembodiment capability of a polymer/inorganic particle composite.

FIG. 7 is a schematic diagram of an embodiment of a polymer/inorganicparticle composite with crosslinked tethered particles.

FIG. 8 is a schematic diagram depicting an inorganic particle forming alinkage through linker compounds with one block of a block copolymer.

FIG. 9 is a schematic diagram depicting a composite formed with twotypes of inorganic particles forming linkages to different blocks of adiblock copolymer.

FIG. 10 is a schematic diagram of integrated devices, at least a portionof which include polymer/inorganic particle composites.

FIG. 11 is a schematic diagram of a coupler including apolymer/inorganic particle composite.

FIG. 12 is a top plan view of a field effect transistor.

FIG. 13 is a side plan view of the field effect transistor of FIG. 9.

FIG. 14 is a perspective view of a laser pyrolysis apparatus used in theproduction of titanium oxide.

FIG. 15 is a cut away side view of the laser pyrolysis apparatus of FIG.14.

FIG. 16 is a sectional view of the laser pyrolysis apparatus of FIG. 14taken along line 16-16 of FIG. 14.

FIG. 17 is a plot of three x-ray diffractograms for each of threedifferent TiO₂ powder samples.

FIG. 18 is a plot of relative ranking for forming dispersions as afunction of solvent dielectric constant.

FIG. 19 is a plot of an absorption spectrum in arbitrary units as afunction of wavelength for a 0.003 weight percent dispersion of TiO₂-1in ethanol.

FIG. 20 is a plot of an absorption spectrum in arbitrary units as afunction of wavelength for a 0.003 weight percent dispersion of TiO₂-2in ethanol.

FIG. 21 is a plot of an absorption spectrum in arbitrary units as afunction of wavelength for a 0.003 weight percent dispersion of TiO₂-3in ethanol.

FIG. 22 is a plot of an absorption spectrum in arbitrary units as afunction of wavelength for a 0.003 weight percent dispersion of onecommercial brand of TiO₂ in ethanol.

FIG. 23 is a plot of an absorption spectrum in arbitrary units as afunction of wavelength for a 0.003 weight percent dispersion of a secondcommercial brand of TiO₂ in ethanol.

FIG. 24 is a plot of Fourier Transform-Infrared Absorption Spectra forpolyacrylic acid alone and two compositions of poly(acrylic acid)titanium oxide composites.

FIG. 25 is a plot of Fourier Transform-Infrared Absorption Spectra forpoly(acrylic acid)-titanium oxide composites treated at three differenttemperatures.

FIG. 26 is a scanning electron micrograph at one magnification of apoly(acrylic acid)-TiO₂ composite formed with a 10 weight percentloading of silylated particles.

FIG. 27 is a scanning electron micrograph of the composite sample inFIG. 26 at a higher magnification.

FIG. 28 is a scanning electron micrograph at one magnification of apoly(acrylic acid)-TiO₂ composite formed with a 10 weight percentloading of untreated particles.

FIG. 29 is a scanning electron micrograph of the composite sample inFIG. 28 at a higher magnification.

FIG. 30 is a scanning electron micrograph at one magnification of apoly(acrylic acid)(2000MW)-TiO₂ composite formed with a 50 weightpercent loading of silylated particles.

FIG. 31 is a scanning electron micrograph of the composite sample inFIG. 30 at a higher magnification.

FIG. 32 is a scanning electron micrograph at one magnification of apoly(acrylic acid)(200MW)-TiO₂ composite formed with a 50 weight percentloading of untreated particles.

FIG. 33 is a scanning electron micrograph of the composite sample inFIG. 32 at a higher magnification.

FIG. 34 is a scanning electron micrograph at one magnification of apoly(acrylic acid)(250,000MW)-TiO₂ composite formed with a 10 weightpercent loading of silylated particles.

FIG. 35 is a scanning electron micrograph of the composite sample inFIG. 34 at a higher magnification.

FIG. 36 is a scanning electron micrograph at one magnification of apoly(acrylic acid)(250,000MW)-TiO₂ composite formed with a 10 weightpercent loading of untreated particles.

FIG. 37 is a scanning electron micrograph of the composite sample inFIG. 36 at a higher magnification.

FIG. 38 is a scanning electron micrograph at one magnification of apoly(acrylic acid)(250,000MW)-TiO₂ composite formed with a 50 weightpercent loading of silylated particles.

FIG. 39 is a scanning electron micrograph of the composite sample inFIG. 38 at a higher magnification.

FIG. 40 is a scanning electron micrograph at one magnification of apoly(acrylic acid)(250,000MW)-TiO₂ composite formed with a 50 weightpercent loading of untreated particles.

FIG. 41 is a scanning electron micrograph of the composite sample inFIG. 40 at a higher magnification.

FIG. 42 is a plot of differential scanning calorimetry measurements fortwo poly(acrylic acid) samples and for two poly(acrylic acid)-TiO₂composites.

FIG. 43 is a scanning electron micrograph one magnification of a film ofpolyamide polymer obtained from the polymerization of 6-amino-caproicacid.

FIG. 44 is a scanning electron micrograph of the film of FIG. 43 at ahigher magnification.

FIG. 45 is a scanning electron micrograph at one magnification of apolyamide-TiO₂ composite formed with a 50 weight percent loading ofuntreated particles.

FIG. 46 is a scanning electron micrograph of the composite of FIG. 45 ata higher magnification.

FIG. 47 is a scanning electron micrograph at one magnification of apolyamide-TiO₂ composite formed with a 50 weight percent loading ofsilylated particles.

FIG. 48 is a scanning electron micrograph of the composite in FIG. 47 ata higher magnification.

FIG. 49 is a plot of Fourier Transform-infrared spectra for twocomposites formed from adipic acid and TiO₂ polymers.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

Composite or hybrid materials generally are formed by chemically bondinga linker compound with both an inorganic nanoparticle and amonomer/polymer unit, although in some embodiments, the polymer isdirectly bonded to the inorganic particle. Through the use of the linkercompound, stable, uniform polymer-inorganic particle composites can beformed with highly dispersed inorganic particles. Specifically, highparticle loadings can be achieved without agglomeration of theparticles, provided that the particles are functionalized with groupsthat do not easily bond to themselves, which can result in the formationof hard agglomerates. The composite may represent a synergistic effectof the combined component. The advantages of the combination can bestructural, electronic or optical.

The composites can be formed as layers on a substrate for the formationof a variety of useful devices, especially optical devices and photoniccrystals. Similarly, the composites can be localized into specificdevices, for example, by self-assembly with appropriate localizationmechanisms. Alternatively, the composites can be formed into freestanding structures, such as fibers.

The composites, thus, include a monomer/polymer component, inorganicparticles, and linker compounds that bridge the inorganic particles andthe monomer/polymer. In the case of monomer units being joined to thelinker compound, a polymer is formed with the formation of thecomposite. For simplicity in notation, the monomer/polymer unit joinedwith the linker and assembled into the composite will be referred togenerally as a polymer, although it is recognized that in some cases theunit can be a monomer or polymer, such as a dimer, trimer or largerpolymer structures.

A range of polymers are suitable for incorporation into the composites,including both organic polymers and inorganic polymers, such aspolysiloxanes. If the polymers are formed prior to reacting with thefunctionalized inorganic particles, the molecular weights of thepolymers can be selected to vary to properties of the resultingcomposite. The polymer is selected or synthesized to include appropriatefunctional groups to covalently bond with functional groups of thelinker compound.

The linker compounds have two or more functional groups. One functionalgroup of the linker is suitable for chemical bonding to the inorganicparticles. Chemical bonding is considered to broadly cover bonding withsome covalent character with or without polar bonding and can haveproperties of ligand-metal bonding along with various degrees of ionicbonding. The functional group is selected based on the composition ofthe inorganic particle, as described further below. Another functionalgroup of the linker is suitable for covalent bonding with the polymer.Covalent bonding refers broadly to covalent bonds with sigma bonds, pibonds, other delocalized covalent bonds and/or other covalent bondingtypes, and may be polarized bonds with or without ionic bondingcomponents and the like. Convenient linkers include functionalizedorganic molecules.

In some embodiments, the polymer incorporates the inorganic particlesinto the polymer network. This can be performed by reacting a functionalgroup of the linker compound with terminal groups of a polymer molecule.Alternatively, the inorganic particles can be present during thepolymerization process such that the functionalized inorganic particlesare directly incorporated into the polymer structure as it is formed. Inother embodiments, the inorganic particles are grafted onto the polymerby reacting the linker functional groups with functional groups onpolymer side groups. In any of these embodiments, the surfacemodified/functionalized inorganic particles can crosslink the polymer ifthere are sufficient linker molecules, i.e., enough to overcomeenergetic barriers and form at least two or more bonded links to thepolymer. Generally, an inorganic particle will have many linkersassociated with the particle. Thus, in practice, the crosslinkingdepends on the polymer-particle arrangement, statistical interaction oftwo crosslinking groups combined with molecular dynamics and chemicalkinetics.

The inorganic particles can be incorporated at a range of loadings intothe composite. Composites with low particle loadings can be producedwith high uniformity. In addition, high inorganic particle loadings ofup to about 50 weight percent or greater can be achieved with welldispersed particles. In addition, the amount the linker compounds bondedto the inorganic particles can be adjusted to vary the degree ofcrosslinking obtained with the polymer.

The inorganic particles generally include metal or metalloid elements intheir elemental form or in compounds. Specifically, the inorganicparticles can include, for example, elemental metal or elementalmetalloid, i.e. un-ionized elements, metal/metalloid oxides,metal/metalloid nitrides, metal/metalloid carbides, metal/metalloidsulfides or combinations thereof Metalloids are elements that exhibitchemical properties intermediate between or inclusive of metals andnonmetals. Metalloid elements include silicon, boron, arsenic, antimony,and tellurium. Preferred particles have an average diameter of less thanabout 500 nanometers (nm). Suitable nanoparticles can be formed, forexample, by flame synthesis, combustion, or sol gel approaches.Preferred methods for synthesizing the particles include laser pyrolysisin which light from an intense focused source drives the reaction toform the particles. Laser pyrolysis is useful in the formation ofparticles that are highly uniform in composition, crystallinity andsize.

To form the desired composites, the inorganic particles are modified ontheir surface by chemical bonding to one or more linker molecules. Theratio of linker composition to inorganic particles preferably is atleast one linker molecular per inorganic particle. The linker moleculessurface modify the inorganic particles, i.e., functionalize theinorganic particles. While the linker molecules bond to the inorganicparticles, they are not necessarily bonded to the inorganic particlesprior to bonding to the polymers. They can be bonded first to thepolymers and only then bonded to the particles. Alternatively, they canbond to the two species simultaneously.

A significant procedure in preferred processes for synthesizing thecomposites involves the dispersion of the inorganic particles in aliquid. The solvent, pH, ionic strength and other additives can beselected to improve the dispersion of the particles. Better dispersionof the particles and stability of the dispersions helps to reduceagglomeration of the particles in the resulting composite.

During formation or after formation of the particle dispersion, thedispersion is interacted with the linker molecules and/or the polymer.Generally, the linker is soluble in the liquid used to form theinorganic particle dispersion and/or the polymer dispersion so that thelinker is homogeneously dissolved when bonding from solution. Conditionsfor the combined particle dispersion and polymer dispersion/solutionshould be suitable for the formation of bonds between the linker, theinorganic particles and the polymer. The order for adding the linker tothe inorganic particles and the polymer can be selected to achieve thedesired processing effectiveness. Once sufficient time has passed tocomplete the bonding between the components of the composite, thecomposite can be processed further.

Once formed, the polymer-inorganic particle composite can be transferredto another solvent or removed from the solvent. The composite can bemolded, extruded, cast or otherwise processed using polymer processingtechnology to form various shapes of materials. In addition, thecomposite can be coated from a solvent based slurry, spin coated or thelike to form a coating of the composite. Any solvent can be removedfollowing the formation of a coating. The coatings can be structuredusing standard mask techniques. In addition, self-assembly techniquescan take advantage of the properties of the components of the compositeto assist with the formation of structures on a substrate, as describedfurther below.

Since a wide range of inorganic particles and polymers can beincorporated into the composites described herein, the composites aresuitable for a wide range of applications. In particular, the compositematerials are useful in the optical and electronics fields. For example,if the inorganic particles have a high index-of-refraction, a variety ofoptical devices or optical coatings can be formed over wide range andcontrollable values of index-of-refraction. For example, the compositescan be used to form high index-of-refraction coatings on optical fibers.High index-of-refraction materials are desirable to control lightpropagation. The index-of-refraction of the composite can be controlledby adjusting particle loading.

Other composites of inorganic particles and polymers have been proposedfor specific applications. For example, U.S. Pat. No. 5,698,309 toDallmann et al., entitled “Molded Bodies Made of Polyester ContainingCovalent-Bonded Oxide Particles,” incorporated herein by reference,discloses molded products including a polyester polymer with oxideparticles. Similarly, U.S. Pat. No. 5,494,949 to Kinkel et al., entitled“Surface-Modified Oxide Particles And Their Use As Fillers An ModifyingAgents In Polymer Materials,” incorporated herein by reference, disclosepolyester-oxide particle composites. In addition, U.S. Pat. No.5,965,299 to Khan et al., entitled “Composite Electrolyte ContainingSurface Modified Fumed Silica,” incorporated herein by reference,discloses a solid lithium electrolyte includes a composite of vinylpolymers and silicon oxide particles. The types of polymers, inorganicparticles, composite structure and/or the types of linkages in thesepatents differ from the corresponding composites and components thereofdescribed in various embodiments herein. In addition, differentapplications and processing approaches have been found forpolymer/inorganic particle composites.

Polymer and Inorganic Particle Composites

The polymer-inorganic particle composites described herein includeinorganic particles bonded to a polymer, preferably through a linkercompound. The linker compound is a multifunctional compound, forexample, a bifunctional compound, that chemically bonds to both theinorganic particle and the polymer. The chemical bonding between thepolymer and the linker generally is covalent. The chemical bondingbetween the linker and the inorganic surface of the particle generallyinvolves a bond of a functional group with the metal atom along withpossible involvement of other atoms in the inorganic composition.

After bonding of the linker to both the polymer and the inorganicparticle, a linkage is formed involving a resulting functional groupjoining the linker compound to the polymer and a second resultingfunctional group joining the linker compound with the inorganicparticle. The resulting or product functional groups are the reactionproducts of the reactions involving the initial linker functionalgroups. Thus, the initial presence of a linker can be identified in theresulting composite by the presence of a plurality of resultingfunctional groups in the linkage between the polymer and the inorganicparticle. The character of the initial linker compound functional groupsmay or may not be uniquely identifiable in the final composite based onthe character of the resulting functional group. More than twofunctional groups can be found on a linkage, for example, if a pluralityof linker molecules are involved, if a linker includes more than twofunctional groups or if the polymer side chain initially includes morethan one functional group.

The inorganic particles can be bonded through the linker compound intothe polymer structure, or the particles can be grafted to polymer sidegroups. The bonded inorganic particles can, in most embodiments,crosslink the polymer. Specifically, most embodiments involve starcrosslinking of a single inorganic particle with several polymer groups.The structure of the composite can generally be controlled by thedensity of linkers, the length of the linkers, the chemical reactivityof the coupling reaction, the density of the reactive groups on thepolymer as well as the loading of particles and the molecular weightrange of the polymer (i.e., monomer/polymer units). In alternativeembodiments, the polymer has functional groups that bond directly withthe inorganic particles, either at terminal sites or at side groups. Inthese alternative embodiments, the polymer includes functional groupscomparable to appropriate linker functional groups for bonding to theinorganic particles.

The composites preferably have stably integrated inorganic particleswell dispersed throughout the composite structure. In this way, highloadings of inorganic particles can be achieved without significantagglomeration of the particles within the composite. Stable compositescan be produced with loadings of greater than about 50 weight percent ofinorganic particles and can be greater than about 80 weight percent. Aperson of ordinary skill in the art will recognize that particleloadings below these specific values are covered within the disclosureherein and are appropriate cut-off values for a range of loadings. Lowloadings, such as one or two percent or less, can be desirable for someapplications.

To form high index-of-refraction materials, high particle loadings aregenerally used. The index-of-refraction of the composite is expected tobe approximately a linear combination by the volume ratios ofindex-of-refraction of the inorganic particles and the polymer. The useof nanoparticles has the advantage for optical materials of highertransparency and reduced scattering of light relative to largerinorganic particles, especially effective in reducing scattering in theinfrared portion of the electromagnetic spectrum including wavelengthsof about 0.8 microns to about 5.0 microns.

Various structures can be formed based on the fundamental idea offorming the chemically bonded polymer/inorganic particle composites. Thestructures obtained will generally depend on the relative amounts ofpolymer/monomers, linkers and inorganic particles as well as thesynthesis process itself. Linkers may be identified also as couplingagents or crosslinkers. A first composite structure is shown in FIG. 1.The composite 100 includes inorganic particles 102, polymer molecules104 and linkers 106. In this embodiment, the inorganic particles haveroughly one linking per particle, which are bonded to the ends of thepolymer molecules. This embodiment is shown for a simple depiction ofthe principles, although in practice, generally many linkers are bondedto each particle to obtained desired levels of polymer bonding to theparticles. Chemical/covalent bonds 108 between moieties are indicatedwith dots.

In the structure shown in FIG. 1, each inorganic particles is bonded toroughly one polymer chain, although there generally will be at least asmall proportion of the inorganic particles bonded to no polymer chainsor more than one polymer chain. Even if there is on average one linkerper inorganic particle, the structure of FIG. 1 may not be formed.Depending on the conditions during the combination of the linker to theinorganic particles, some inorganic particles can be bonded to two ormore linkers while other inorganic particles may not be bonded to anylinkers.

In addition, the relative amounts of polymer and surface modifiedparticles influences whether a polymer molecule is bonded on both endsor only on a single end with an inorganic molecule and linker. Forexample, if the polymers are present in significantly higherequivalence/molarity, most polymer molecules will have at most onebonded inorganic particles. Again, however, the amount of mixing andother processing parameters can influence the ultimate structure.

In general, a large number of crosslinking molecules are bonded to eachof the inorganic particles. With a reasonable portion of the linkersbonding to a polymer, the inorganic particles with bonded linkerscrosslink the polymers. For example, a structure involving crosslinkedinorganic particles is shown in FIG. 2. In this embodiment, composite 10includes a majority of the inorganic particles 102 that are bonded to aplurality of linkers 106. The linker modified inorganic particles thenfunction to crosslink polymer molecules 104. A representative set ofcomponent labels are shown. Ellipsis marks are used to indicatecontinuing crosslinked structure.

The major difference between the structure of FIG. 1 and the structureof FIG. 2 involves the relative amount of linking. The structure in FIG.1 has approximately one linker molecule per inorganic particle, whilethe structure in FIG. 2 has more than one linker per inorganic particle.As noted above, even if there are roughly one linker per inorganicparticle, the surface modified inorganic particles can crosslink thepolymer if the surface modification of the particles is performed underconditions in which many particles are bonded with more than one linkermolecule while other particles are bonded to no linkers. The detailedstructure of a crosslinked polymer, as shown in FIG. 2, will depend onthe relative amounts of linker, inorganic particles, and polymermolecules as well as the size of the linker, the chemical reactivity ofthe linker and the processing conditions. The linker can have more thantwo functional groups, such that the linker can also crosslink thecomposite.

In preferred embodiments, the linker is applied to form at least asignificant fraction of a monolayer on the surface of the particles. Inparticular, preferably at least about 20% of a monolayer is applied tothe particles, and generally at least about 40% of a monolayer isapplied. A monolayer is calculated based on measured surface area of theparticles and an estimate of the molecular radius of the linker based onaccepted values of the atomic radii. With these high linker coverages,the linkers presumably form a highly crosslinked structure with thepolymers. At each inorganic particle, star crosslinking structures areformed. This is shown schematically in FIG. 3, in which inorganicparticle 102 is bonded to a number of linkers 106 that are in turnbonded to polymers 104. A highly crosslinked structure results aroundthe star linkages at the inorganic particles. These structures areexpected to be related also to low particle concentration or polymergrowth initiated from the particle surface.

Another composite structure 112 is shown in FIG. 4 in which thepolymerization takes place in the presence of the surface modifiedinorganic particles. The particles become an integral part of thepolymer structure. A plurality of different monomer units can be used,such that a copolymer is formed. Using appropriately selected functionalgroups and/or polymerization conditions to form sequentialpolymerization, block copolymers can be formed. Block copolymerstructures are described further below. In the embodiment in FIG. 4, therelative amount of monomers 114 relative to the inorganic particles 102and linkers 106 determines the precise structure. As shown in FIG. 4,monomers 114 bond to other monomers 114 or to linkers 106. Inalternative embodiments, the monomers can include functional groups thatbond to just linker molecules and not to other monomers. In such analternative structure, the surface modified inorganic particles areintegral to the formation of a polymer structure in which the inorganicparticles and linkers function as repeat units within the polymer.

The degree of crosslinking in composite 112 of FIG. 4 depends on therelative amount of linker compared with inorganic particles and monomer.In addition, the monomers can include the capability to crosslinkbetween themselves by having the capability of forming three or morecovalent bonds. Thus, a variety of structures can be formed. In FIG. 4only a representative sample of label numbers are shown for clarity, andellipsis marks are used to indicate further structure.

An embodiment of a composite with grafted inorganic particles is shownin FIG. 5. Composite 140 includes polymer 142 with monomers 144 havingfunctional side groups 146. Side groups 146 are covalently bonded tolinkers 106 that are chemically bonded to inorganic particles 102. Ofcourse, if insufficient quantities of surface modified inorganicparticles are available or if the frequency of the side groups is high,as with polyacrylic acid, all side groups 146 may not be bonded tolinkers 106 attached to inorganic particles 102.

An alternative embodiment is shown in FIG. 6. In the embodiment in FIG.6, composite 160 includes a copolymer 162 comprising monomers 164 withfunctional side groups 166 and monomers 168 without functional sidegroups. The degree of grafting with inorganic particles can becontrolled by the relative amounts of monomers with functional sidegroups relative to the total number of monomers.

If the amount of linker molecules are increased, the grafted inorganicparticles can also form crosslinks between polymer chains. Referring toFIG. 7, composite 180 includes polymer molecules 182 with monomers 184having functional side groups 186 and monomers 188 without functionalside groups. Inorganic particles 102 with linkers 106 can be crosslinkedbetween two functionalized side groups. The degree of crosslinkingdepends on the relative amounts of all of the constituents.

In all of the structures of FIGS. 1-7, the ability exists to form blockcopolymers. For example, the polymer chains bonding to the linkers canthemselves be block copolymers. Thus, the resulting structure is a blockcopolymer tethered with inorganic particles. In one form, the inorganicparticles bonded to the linkers can crosslink the block copolymers withstar linkages of FIG. 3. Such a block copolymer is shown in FIG. 8.Inorganic particles 200 are bonded to linkers 202. Linkers 202 arebonded to block copolymers 204 with blocks 206, 208.

As shown in FIG. 8, the inorganic particles crosslink the composite bybonding to the polymers through side groups of the copolymers.Generally, the inorganic particles can bond to side groups of only oneor of both blocks of the polymer. As shown in FIG. 8, the inorganicpolymers are only grafted to block 206 of copolymers 204.

In other alternative embodiments, each block can bond to different typesof modified inorganic particles. For example, one type of inorganicparticle can be bonded to one linker molecule while a second type ofinorganic particle is bonded to a second type of linker. One linker hasan appropriate functional group to bond with one block of the blockcopolymer, and the second linker has an appropriate functional group tobond with the other block of the block copolymer.

Such a copolymer is shown in FIG. 9. The composite includes a first typeof inorganic particle 220 and a second type of inorganic particle 222.The different types of particles can differ by composition, crystalstructure and/or physical properties. Inorganic particles 220 are bondedto first linkers 224, and inorganic particles 222 are bonded to secondlinkers 226. Linkers 224 are bonded to a first block 228 of blockcopolymer 230, and linkers 226 are bonded to a second block 232 of blockcopolymer 230.

If the chemical compositions of the different blocks are selected to bechemically different with respect to charge, polarity, hydrophobicity,and the like, the blocks may tend to segregate in solution. Thissegregation is a form of self-organization. Self-organization propertiescan be exploited in performing self-assembly.

The difference in properties between the various embodiments will dependon the details of the chemical moieties, the relative amounts of theconstituents and the structure of the composite. Representativeembodiments of the composites have been described. Clearly, othervariations in composite structures incorporating various features can beconstructed by combining and/or varying the features of the variouscomposite structures described. The precise composite structure willdepend on the nature of the polymer and linker, the relative amounts ofthe components and the processing conditions.

The inorganic particles are selected to yield desired properties for theresulting composite materials. For example, the inorganic particles canbe selected based on, for example, their optical properties, electricalconductivity, electronic/magnetic properties, thermal properties, suchas thermal expansion, luminescence or catalytic activity. Suitableinorganic particles include, for example, metal/metalloid particles,metal/metalloid oxides, metal/metalloid nitrides, metal/metalloidcarbides, metal/metalloid sulfides, metal/metalloid phosphates andmixtures thereof Details about preferred properties and approaches forsynthesizing preferred inorganic particles are presented in thefollowing section.

Suitable polymers include organic polymers, silicon based polymers andother inorganic polymers. Many different types of polymers are suitableas long as they have terminal groups and/or preferably side groupscapable of bonding to a linker. Suitable organic polymers include, forexample, polyamides (nylons), polyimides, polycarbonates, polyurethanes,polyacrylonitrile, polyacrylic acid, polyacrylates, polyacrylamides,polyvinyl alcohol, polyvinyl chloride, heterocyclic polymers, polyestersand modified polyolefins. Composites formed with nylon polymers, i.e.,polyamides, and inorganic nanoparticles can be called Nanonylon™.Suitable polymers include conjugated polymers within the polymerbackbone, such as polyacetylene, and aromatic polymers within thepolymer backbone, such as poly(p-phenylene), poly(phenylene vinylene),polyaniline, polythiophene, poly(phenylene sulfide), polypyrrole andcopolymers and derivatives thereof. Some polymers can be bonded tolinkers at functional side groups. The polymer can inherently includedesired functional groups, can be chemically modified to introducedesired functional groups or copolymerized with monomer units tointroduce a portions of desired functional groups. Electricallyconducting polymers can be particularly useful for certain applications.Polyacetylene becomes an electrical conductor upon doping with electronacceptors, such as halogens, or electron donors, such as alkali metals.Mixtures of polymers can also be used, although in many embodiments oneof the above polymers is present in at least about 50% by weight,optionally at least about 75% by weight and optionally at least about90% by weight of the polymer/monomer composition. Similarly, somecomposites include only a single polymer/monomer composition bonded intothe composite. Within a crosslinked structure, a polymer is identifiableby 3 or more repeat units along a chain, except for hydrocarbon chainswhich are not considered polymers unless they have a repeating sidegroup or at least about 50 carbon-carbon bonds within the chain.

Preferred silicon-based polymers include polysilanes and polysiloxane(silicone) polymers, such as poly(dimethylsiloxane) (PDMS).Polysiloxanes are particularly suitable for forming composites withgrafted inorganic particles. To form these grafted composites, thepolysiloxanes can be modified with amino and/or carboxylic acid groups.Polysiloxanes are desirable polymers because of their transparency tovisible and ultraviolet light, high thermal stability, resistance tooxidative degradation and its hydrophobicity. Other inorganic polymersinclude, for example, phosphazene polymers (phosphonitrile polymers).

Polyamides are desirable since unreacted carboxylic acid groups or aminegroups can be used to covalently bond the polymer to the linkercompound. Various polyamides are commercially available and havedesirable mechanical properties, such as the Nylon 6. Polyimides are ofinterest because of their excellent structural and thermal properties.In particular, some polyimides have very high thermal stability. Somefluorinated polyimides are curable under ultraviolet light for lowtemperature processing. In addition, some polyimides are at least partlytransparent to infrared light. In addition, polyimides can have liquidcrystal properties. Polyimides can bond to various functional groups oflinker either directly or through functional side groups.

Vinyl polymers are attractive because of their low cost and flexibilitywith respect to selecting desired side group properties, due to the manydifferent vinyl polymers available. Vinyl polymers can be synthesized byradical initiation. Acrylic polymers are of particular interest becauseof their transparency and side group functionalities. In addition,acrylic polymers can be copolymerized into block copolymers, which canbe used to form organized nanoscale structures.

The linkers are polyfunctional molecules that have at least onefunctional group that bonds to the inorganic particles and at least onefunctional group that bonds to the polymer. The functional groups arepreferably positioned in the linker molecule such that there is nostearic interference with the bonding to both the inorganic particle andthe polymer. Thus, the linker provides bonding capability that leads tothe complex formation. In preferred embodiments, the functional groupsintended to bind with the inorganic particles are chemically andfunctionally distinct from the functional groups that bind to thepolymer such that the linkers do not just crosslink polymers orinorganic particles together without forming the composite. The linkercan include more than two functional groups such that the linker canform chemical crosslinks within the composite. Also, the linker shouldbe treated in a mode that reduces, preferably as much as possible,self-condensation of the linker. This is particularly relevant in thecase of multi-alkoxy or multi-chloro silanes that can polycondense toform oligomeric or resin-like crosslinkers.

The frame of the linker supporting the functional groups is generally anorganic compound, although it may also include silyl and/or siloxymoieties. The organic linker frame can comprise any reasonable organicmoiety including, for example, linear or branched carbon chains,cyclical carbon moieties, saturated carbon moieties, unsaturated carbonmoieties, aromatic carbon units, halogenated carbon groups andcombinations thereof. The structure of the linker can be selected toyield desirable properties of the composite. For example, the size ofthe linker is a control parameter that may effect the periodicity of thecomposite and the self-organization properties.

Appropriate functional groups for binding with the polymer depend on thefunctionality of the polymer. Generally, the functional groups of thepolymers and the linker can be selected appropriately based on knownbonding properties. For example, carboxylic acid groups bond covalentlyto thiols, amines (primary amines and secondary amines) and alcoholgroups. As a particular example, nylons can include unreacted carboxylicacid groups, amine groups or derivatives thereof that are suitable formcovalently bonding to linkers. In addition, for bonding to acrylicpolymers, a portion of the polymer can be formed from acrylic acid orderivatives thereof such that the carboxylic acid of the acrylic acidcan bond with amines (primary amines and secondary amines), alcohols orthiols of a linker. The functional groups of the linker can provideselective linkage either to only particles with particular compositionsand/or polymers with particular functional groups. Other suitablefunctional groups for the linker include, for example, halogens, silylgroups (—SiR_(3-x)H_(x)), isocyanate, cyanate, thiocyanate, epoxy, vinylsilyls, silyl hydrides, silyl halogens, mono-, di- andtrihaloorganosilane, phosphonates, organometalic carboxylates, vinylgroups, allyl groups and generally any unsaturated carbon groups(—R′—C═C—R″), where R′ and R″ are any groups that bond within thisstructure. Selective linkage can be useful in forming compositestructures that exhibit self-organization.

Upon reaction of the polymer functional groups with the linkerfunctional groups, the identity of initial functional groups is mergedinto a resultant or product functional group in the bonded structure. Alinkage is formed that extends from the polymer. The linkage extendingfrom the polymer can include, for example, an organic moiety, a siloxymoiety, a sulfide moiety, a sulphonate moiety, a phosphonate moiety, anamine moiety, a carbonyl moiety, a hydroxyl moiety, or a combinationthereof. The identity of the original functional groups may or may notbe apparent depending on the resulting functional group. The resultingfunctional groups generally can be, for example, an ester group, anamide group, an acid anhydride group, an ether group, a sulfide group, adisulfide group, an alkoxy group, a hydrocarbyl group, a urethane group,an amine group, an organo silane group, a hydridosilane group, a silanegroup, an oxysilane group, a phosphonate group, a sulphonate group or acombination thereof.

If a linker compound is used, one resulting functional group generallyis formed where the polymer bonds to the linker and a second resultingfunctional group is formed where the linker bonds to the inorganicparticle. At the inorganic particle, the identification of thefunctional group may depend on whether particular atoms are associatedwith the particle or with the functional group. This is just anomenclature issue, and a person of skill in the art can identify theresulting structures without concern about the particular allocation ofatoms to the functional group. For example, the bonding of a carboxylicacid with an inorganic particle may result in a group involving bondingwith a non-metal/metalloid atom of the particle; however, an oxo groupis generally present in the resulting functional group regardless of thecomposition of the particle. Ultimately, a bond extends to ametal/metalloid atom.

Appropriate functional groups for bonding to the inorganic particlesdepends on the character of the inorganic particles. U.S. Pat. No.5,494,949 to Kinkel et al., entitled “Surface-Modified Oxide ParticlesAnd Their Use As Fillers And Modifying Agents In Polymer Materials,”incorporated herein by reference, describes the use of silylating agentsfor bonding to metal/metalloid oxide particles. The particles havealkoxy modified silane for bonding to the particles. For example,preferred linkers for bonding to metal/metalloid oxide particles includeR¹R²R³—Si—R⁴, where R¹, R², R³ are alkoxy groups, which can hydrolyzeand bond with the particles, and R⁴ is a group suitable for bonding tothe polymer. Trichlorosilicate (—SiCl₃) functional groups can react withan hydroxyl group at the metal oxide particle surface by way of acondensation reaction.

Generally, thiol groups can be used to bind to metal sulfide particlesand certain metal particles, such as gold, silver, cadmium and zinc.Carboxyl groups can bind to other metal particles, such as aluminum,titanium, zirconium, lanthanum and actinium. Similarly, amines andhydroxide groups would be expected to bind with metal oxide particlesand metal nitride particles, as well as to transition metal atoms, suchas iron, cobalt, palladium and platinum.

The identity of the linker functional group that bonds with theinorganic particle may also be modified due to the character of thebonding with the inorganic particle. One or more atoms of the inorganicparticle are involved in forming the bond between the linker and theinorganic particle. It may be ambiguous if an atom in the resultinglinkage originates from the linker compound or the inorganic particle.In any case, a resulting or product functional group is formed joiningthe linker molecule and the inorganic particle. The resulting functionalgroup can be, for example, one of the functional groups described aboveresulting from the bonding of the linker to the polymer. The functionalgroup at the inorganic particle ultimately bonds to one or moremetal/metalloid atoms.

Inorganic Particles

In general, any reasonable inorganic particles can be used to form thecomposites. In preferred embodiments, the particles have an averagediameter of no more than about one micron. For preferred applicationsthe composition of the particles is selected to impart desiredproperties to the composite. In particular, for composites with highparticle loadings, the inorganic particles contribute significantly tothe overall properties of the composite. Thus, in the formation ofoptical materials for example, the optical properties of both thepolymer and the inorganic particles can be significant. It is expectedthat the index-of-refraction of the composite material is roughly thelinear combination based on the volume ratios of theindex-of-refractions of the inorganic particles and the polymer.

Preferred particles are formed by laser pyrolysis, which can be used toform a range of submicron particles with extremely uniform properties.Small particles can provide processing advantages with respect toforming small structures and smooth surfaces. In addition, smallparticles have desirable properties including reduced scattering tolower scattering loss.

A collection of particles of interest generally has an average diameterfor the primary particles of less than about 500 nm, preferably fromabout 2 nm to about 100 nm, alternatively from about 2 nm to about 75nm, or from about 2 nm to about 50 nm. A person of ordinary skill in theart will recognize that other ranges within these specific ranges arecovered by the disclosure herein. Particle diameters are evaluated bytransmission electron microscopy. Preferred particles compriseelemental/non-ionic metal/metalloid, a metal/metalloid oxide, ametal/metalloid nitride, a metal/metalloid sulfide, a metal/metalloidcarbide or combinations thereof.

The primary particles can have a roughly spherical gross appearance, orthey can have rod shapes, plate shapes or other non-spherical shapes.Upon closer examination, crystalline particles generally have facetscorresponding to the underlying crystal lattice. Amorphous particlesgenerally have a spherical aspect. Diameter measurements on particleswith asymmetries are based on an average of length measurements alongthe principle axes of the particle.

Because of their small size, the primary particles tend to form looseagglomerates due to van der Waals and other electromagnetic forcesbetween nearby particles. These agglomerates can be dispersed to asignificant degree, as described further below. The secondary oragglomerated particle size depends on the subsequent processing of theparticles following their initial formation and the composition andstructure of the particles. In preferred embodiments, the secondaryparticles have an average diameter from about 2 nm to about 400 nm,preferably about 2 nm to about 100 nm, alternatively about 2 nm to about50 nm. A person of ordinary skill in the art will recognize that otherranges within these specific ranges are covered by the disclosureherein.

Even though the particles form loose agglomerates, the nanometer scaleof the primary particles is clearly observable in transmission electronmicrographs of the particles. The particles generally have a surfacearea corresponding to particles on a nanometer scale as observed in themicrographs. Furthermore, the particles can manifest unique propertiesdue to their small size and large surface area per weight of material.For example, vanadium oxide nanoparticles can exhibit surprisingly highenergy densities in lithium batteries, as described in U.S. Pat. No.5,952,125 to Bi et al., entitled “Batteries With ElectroactiveNanoparticles,” incorporated herein by reference.

The primary particles preferably have a high degree of uniformity insize. Laser pyrolysis, as described above, generally results inparticles having a very narrow range of particle diameters. Furthermore,heat processing under suitably mild conditions does not alter the verynarrow range of particle diameters. With aerosol delivery of reactantsfor laser pyrolysis, the distribution of particle diameters isparticularly sensitive to the reaction conditions. Nevertheless, if thereaction conditions are properly controlled, a very narrow distributionof particle diameters can be obtained with an aerosol delivery system.As determined from examination of transmission electron micrographs, theprimary particles generally have a distribution in sizes such that atleast about 95 percent, and preferably 99 percent, of the primaryparticles have a diameter greater than about 40 percent of the averagediameter and less than about 160 percent of the average diameter.Preferably, the primary particles have a distribution of diameters suchthat at least about 95 percent, and preferably 99 percent, of theprimary particles have a diameter greater than about 60 percent of theaverage diameter and less than about 140 percent of the averagediameter. A person of ordinary skill in the art will recognize thatother ranges within these specific ranges are covered by the disclosureherein.

Furthermore, in preferred embodiments no primary particles have anaverage diameter greater than about 4 times the average diameter andpreferably 3 times the average diameter, and more preferably 2 times theaverage diameter. In other words, the particle size distributioneffectively does not have a tail indicative of a small number ofparticles with significantly larger sizes. This is a result of the smallreaction region and corresponding rapid quench of the particles. Aneffective cut off in the tail of the size distribution indicates thatthere are less than about 1 particle in 10⁶ have a diameter greater thana specified cut off value above the average diameter. High particleuniformity can be exploited in a variety of applications.

In addition, the nanoparticles preferably have a very high purity level.The nanoparticles produced by laser pyrolysis are expected to have apurity greater than the reactants because the laser pyrolysis reactionand, when applicable, the crystal formation process tends to excludecontaminants from the particle. Furthermore, crystalline nanoparticlesproduced by laser pyrolysis have a high degree of crystallinity.Similarly, the crystalline nanoparticles produced by heat processinghave a high degree of crystallinity. Impurities on the surface of theparticles may be removed by heating the particles to achieve not onlyhigh crystalline purity but high purity overall.

Laser pyrolysis is an excellent approach for efficiently producing awide range of nanoscale particles with a narrow distribution of averageparticle diameters. In particular, laser pyrolysis can be used toproduce a variety of inorganic particles, such as elementalmetal/metalloid particles, metal/metalloid oxide particles,metal/metalloid carbide particles, metal/metalloid nitride particles andmetal/metalloid sulfide particles. Alternatively, submicron particlescan be produced using a flame production apparatus such as the apparatusdescribed in U.S. Pat. No. 5,447,708 to Helble et al., entitled“Apparatus for Producing Nanoscale Ceramic Particles,” incorporatedherein by reference. Furthermore, submicron particles can be producedwith a thermal reaction chamber such as the apparatus described in U.S.Pat. No. 4,842,832 to Inoue et al., “Ultrafine Spherical Particles ofMetal Oxide and a Method for the Production Thereof,” incorporatedherein by reference. In addition, various solution based approaches canbe used to produce submicron particles, such as sol gel techniques.

A basic feature of successful application of laser pyrolysis for theproduction of desirable inorganic nanoparticles is the generation of areactant stream containing a metal/metalloid precursor compound, aradiation absorber and, generally, a secondary reactant. The secondaryreactant can be a source of atoms, such as oxygen, required for thedesired product or an oxidizing or reducing agent to drive a desiredproduct formation. A secondary reactant is not needed if the precursordecomposes to the desired product under intense light radiation.Similarly, a separate radiation absorber is not needed if themetal/metalloid precursor and/or the secondary reactant absorb theappropriate light radiation. The reactant stream is pyrolyzed by anintense light beam, generally a laser beam. As the reactant streamleaves the laser beam, the particles are rapidly quenched.

A laser pyrolysis apparatus suitable for the production of commercialquantities of particles by laser pyrolysis has been developed using areactant inlet that is significantly elongated in a direction parallelto the path of the laser beam. This high capacity laser pyrolysisapparatus is described in U.S. Pat. No. 5,958,348, entitled “EfficientProduction Of Particles By Chemical Reaction,” incorporated herein byreference. Approaches for the delivery of aerosol precursors forcommercial production of particles by laser pyrolysis is described incopending and commonly assigned U.S. patent application Ser. No.09/188,670, now U.S. Pat. No. 6,193,936 to Gardner et al., entitled“Reactant Delivery Apparatus,” incorporated herein by reference.

Nanoparticles produced by laser pyrolysis can be subjected to additionalprocessing to alter the nature of the particles, such as the compositionand/or the crystallinity. For example, the nanoparticles can besubjected to heat processing in a gas atmosphere prior to use. Undersuitably mild conditions, heat processing is effective to modify thecharacteristics of the particles without destroying the nanoscale sizeor the narrow particle size distribution of the initial particles. Forexample, heat processing of submicron vanadium oxide particles isdescribed in U.S. Pat. No. 5,989,514 to Bi et al., entitled “ProcessingOf Vanadium Oxide Particles With Heat,” incorporated herein byreference.

Several different types of submicron or nanoscale particles have beenproduced by laser pyrolysis with or without additional heat processing.These particles generally have a very narrow particle size distribution,as described above.

In particular, the production of vanadium oxide nanoparticles isdescribed in U.S. Pat. No. 6,106,798 to Bi et al., entitled “VanadiumOxide Nanoparticles,” incorporated herein by reference. Similarly,silver vanadium oxide nanoparticles have been produced, as described incopending and commonly assigned U.S. patent application Ser. No.09/246,076 to Home et al., now U.S. Pat. No. 6,225,007 and Ser. No.09/311,506, now U.S. Pat. No. 6,394,494 to Reitz et al., both entitled“Metal Vanadium Oxide Particles,” both of which are incorporated hereinby reference.

Also, nanoscale manganese oxide particles have been formed by laserpyrolysis. The production of these particles is described in copendingand commonly assigned U.S. patent application Ser. No. 09/188,770, nowU.S. Pat. No. 6,506,493 to Kumar et al., entitled “Metal OxideParticles,” incorporated herein by reference. This application describesthe production of MnO, Mn₂O₃, Mn₃O₄ and Mn₅O₈.

Furthermore, lithium manganese oxide nanoparticles have been produced bylaser pyrolysis along with or without subsequent heat processing, asdescribed in copending and commonly assigned U.S. patent applicationSer. No. 09/188,768, now U.S. Pat. No. 6,607,706 to Kumar et al.,entitled “Composite Metal Oxide Particles,” and Ser. No. 09/334,203, nowU.S. Pat. No. 6,482,374 to Kumar et al., entitled “Reaction Methods forProducing Ternary Particles,” and U.S. Pat. No. 6,136,287 to Home etal., entitled “Lithium Manganese Oxides and Batteries,” all three ofwhich are incorporated herein by reference.

The production of silicon oxide nanoparticles is described in copendingand commonly assigned U.S. patent application Ser. No. 09/085,514, nowU.S. Pat. No. 6,726,990 to Kumar et al., entitled “Silicon OxideParticles,” incorporated herein by reference. This patent applicationdescribes the production of amorphous SiO₂. The synthesis by laserpyrolysis of silicon carbide and silicon nitride is described incopending and commonly assigned U.S. patent application Ser. No.09/433,202 to Reitz et al. filed on Nov. 5, 1999, entitled “ParticleDispersions,” incorporated herein by reference.

The production of titanium oxide nanoparticles is described in copendingand commonly assigned, U.S. patent application Ser. No. 09/123,255, nowU.S. Pat. No. 6,387,531 to Bi et al., entitled “Metal (Silicon)Oxide/Carbon Composites,” incorporated herein by reference. Inparticular, this application describes the production of anatase andrutile TiO₂. The production of aluminum oxide nanoparticles is describedin copending and commonly assigned, U.S. patent application Ser. No.09/136,483 to Kumar et al., entitled “Aluminum Oxide Particles,”incorporated herein by reference. In particular, this applicationdisclosed the production of ã-Al₂O₃. Suitable liquid, aluminumprecursors with sufficient vapor pressure of gaseous delivery include,for example, aluminum s-butoxide (Al(OC₄H₉)₃). Also, a number ofsuitable solid, aluminum precursor compounds are available including,for example, aluminum chloride (AlCl₃), aluminum ethoxide (Al(OC₂H₅)₃),and aluminum isopropoxide (Al[OCH(CH₃)₂]₃).

In addition, tin oxide nanoparticles have been produced by laserpyrolysis, as described in copending and commonly assigned U.S. patentapplication Ser. No. 09/042,227, now U.S. Pat. No. 6,200,674 to Kumar etal., entitled “Tin Oxide Particles,” incorporated herein by reference.The production of zinc oxide nanoparticles is described in copending andcommonly assigned U.S. patent application Ser. No. 09/266,202 to Reitz,entitled “Zinc Oxide Particles,” incorporated herein by reference. Inparticular, the production of ZnO nanoparticles is described.

The production of iron and iron carbide is described in a publication byBi et al., entitled “Nanocrystalline á-Fe, Fe₃C, and Fe₇C₃ produced byCO₂ laser pyrolysis,” J. Mater. Res. Vol. 8, No. 7 1666-1674 (July1993), incorporated herein by reference. The production of iron oxidenanoparticles is described in U.S. Pat. No. 6,080,337 to Kambe et al.,entitled “Iron Oxide Particles,” incorporated herein by reference. Theproduction of nanoparticles of silver metal is described in copendingand commonly assigned U.S. patent application Ser. No. 09/311,506, nowU.S. Pat. No. 6,394,494 to Reitz et al., entitled “Metal Vanadium OxideParticles,” incorporated herein by reference.

The production of iron sulfide (Fe_(1-x)S) nanoparticles by laserpyrolysis is described in Bi et al., Material Research Society SymposiumProceedings, vol 286, p. 161-166 (1993), incorporated herein byreference. Precursors for laser pyrolysis production of iron sulfidewere iron pentacarbonyl (Fe(CO)₅) and hydrogen sulfide (H₂S).

Cerium oxide can also be produced using laser pyrolysis. Suitableprecursors for aerosol delivery include, for example, cerous nitrate(Ce(NO₃)₃), cerous chloride (CeCl₃) and cerous oxalate (Ce₂(C₂O₄)₃).Similarly, zirconium oxide can be produced using laser pyrolysis.Suitable zirconium precursors for aerosol delivery include, for example,zirconyl chloride (ZrOCl₂) and zirconyl nitrate (ZrO(NO₃)₂).

The production of ternary nanoparticles of aluminum silicate andaluminum titanate can be performed by laser pyrolysis followingprocedures similar to the production of silver vanadium oxidenanoparticles described in copending and commonly assigned U.S. patentapplication Ser. No. 09/311,506, now U.S. Pat. No. 6,394,494 to Reitz etal., entitled “Metal Vanadium Oxide Particles,” incorporated herein byreference. Suitable precursors for the production of aluminum silicateinclude, for vapor delivery, a mixture of aluminum chloride (AlCl₃) andsilicon tetrachloride (SiCl₄) and, for aerosol delivery, a mixture oftetra(N-butoxy) silane and aluminum isopropoxide (Al(OCH(CH₃)₂)₃).Similarly, suitable precursors for the production of aluminum titanateinclude, for aerosol delivery, a mixture of aluminum nitrate (Al(NO₃)₃)and titanium dioxide (TiO₂) powder dissolved in sulfuric acid or amixture of aluminum isopropoxide and titanium isopropoxide(Ti(OCH(CH₃)₂)₄).

Particle Dispersions

To form the composites, generally the inorganic particles are dispersedin a liquid and combined with polymer/monomers constituents and thelinker. The formation of the particle dispersion generally is a distinctstep of the process. Preferably, a collection of nanoparticles is welldispersed for uniform introduction into a polymer composite. A liquidphase particle dispersion can provide a source of small secondaryparticles that can be used in the formation of desirable compositestructures.

Desirable qualities of a liquid dispersion of inorganic particlesgenerally depend on the concentration of particles, the composition ofthe dispersion and the formation of the dispersion. Specifically, thedegree of dispersion intrinsically depends on the interparticleinteractions, the interactions of the particles with the liquid and thesurface chemistry of the particles. Both entropic and energeticconsideration may be involved. The degree of dispersion and stability ofthe dispersion can be significant features for the production of uniformcomposites without large effects from significantly agglomeratedparticles.

Generally, the liquid dispersions refer to dispersions having particleconcentrations of no more than about 80 weight percent. For theformation of a particle dispersion, the particular particleconcentration depends on the selected application. At concentrationsgreater than about 50 weight percent, different factors can besignificant with respect to the formation and characterization of theresulting viscous blend relative to parameters that characterize themore dilute particle dispersions. The concentration of particles affectsthe viscosity and can effect the efficacy of the dispersion process. Inparticular, high particle concentrations can increase the viscosity andmake it more difficult to disperse the particles to achieve smallsecondary particle sizes, although the application of shear can assistwith particle dispersion.

The composition of the dispersion depends on the composition of thedispersant and the nanoparticles. Suitable dispersants include, forexample, water, organic solvents, such as alcohols and hydrocarbons, andcombinations thereof. The selection of preferred solvents generallydepends on the properties of the nanoparticles. Thus, the dispersant andthe nanoparticles should be selected to be compatible for the formationof well dispersed particles. For example, gamma alumina particlesgenerally are dispersed well at acidic pH values of about 34, silicaparticles generally are dispersed well at basic pH values from 9-11, andtitanium oxide particles generally disperse well at a pH near 7,although the preferred pH depends on the crystal structure and thesurface structure. Generally, nanoparticles with little surface chargecan be dispersed preferentially in less polar solvents. Thus,hydrophobic particles can be dispersed in nonaqueous solvents or aqueoussolutions with less polar cosolvents, and hydrophilic particles can bedispersed in aqueous solvent.

Since many polymers are soluble in organic solvents, many embodimentsinvolve the formation of non-aqueous dispersions. In organic solvents,the dispersion properties have been found to depend on the solventdielectric constant. For TiO₂, good dispersions are formed withintermediate values of solvent dielectric constants/polarity. This isdescribed further in the examples below.

In addition, water based dispersions can include additionalcompositions, such as surfactants, buffers and salts. For particularparticles, the properties of the dispersion can be adjusted by varyingthe pH and/or the ionic strength. Ionic strength can be varied byaddition of inert salts, such as sodium chloride, potassium chloride orthe like. The presence of the linker can effect the properties andstability of the dispersion. For TiO₂, this is described in the examplesbelow.

The pH generally effects the surface charge of the dispersed particles.The minimum surface charge is obtained at pH value of the isoelectricpoint. A decrease in surface charge can result in further agglomeration.Thus, it may be useful to select the pH to yield a desired amount ofsurface charge based on subsequent processing steps. However, the pH ofthe solution can affect binding with the linker.

The liquid may apply physical/chemical forces in the form ofsolvation-type interactions to the particles that may assist in thedispersion of the particles. Solvation-type interactions can beenergetic and/or entropic in nature. Additional compositions, such assurfactants, can be added to the liquid to assist with the dispersionfor the particles. Suitable surfactants include, for example, octoxynol(sold as Triton® X), nonxynol (sold as Doxfax® 9N and Triton® N), anddodecyltrimethyl ammonium bromide (C12 TAB, CH₃(CH₂)₁₁N(CH₃)₃Br).

The qualities of the dispersion generally depend on the process for theformation of the dispersion. In dispersions, besides chemical/physicalforces applied by the dispersant and other compounds in the dispersion,mechanical forces can be used to separate the primary particles, whichare held together by van der Waals forces and other short rangeelectromagnetic forces between adjacent particles. In particular, theintensity and duration of mechanical forces applied to the dispersionsignificantly influences the properties of the dispersion. Mechanicalforces can be applied to the powders prior to dispersion in a solvent.Alternatively, mechanical forces, such as shear stress, can be appliedas mixing, agitation, jet stream collision and/or sonication followingthe combination of a powder or powders and a liquid or liquids.

The secondary particle size refers to the size of the resulting particleagglomerates following dispersion of the powders in the liquid. Smallersecondary particles sizes are obtained if there is more disruption ofthe agglomerating forces between the primary particles. Secondaryparticles sizes equal to the primary particle sizes can be accomplishedwith at least some nanoparticles if the interparticle forces can besufficiently disrupted. The use of surfactants and high shear stress canassist with obtaining smaller secondary particle sizes.

Secondary particles sizes within a liquid dispersion can be measured byestablished approaches, such as dynamic light scattering. Suitableparticle size analyzers include, for example, a Microtrac UPA instrumentfrom Honeywell based on dynamic light scattering and ZetaSizer Series ofinstruments from Malvern based on Photon Correlation Spectroscopy. Theprinciples of dynamic light scattering for particle size measurements inliquids are well established.

The presence of small secondary particle sizes can result in significantadvantages in the application of the dispersions for the formation ofcomposites with uniform properties. For example, smaller secondaryparticle sizes, and generally small primary particle sizes, may assistwith the formation of smoother and/or smaller and more uniformstructures using the composites. In the formation of coatings, thinnerand smoother coatings can be formed with composites formed withinorganic particle dispersions having smaller secondary particles. Inpreferred embodiments, the average secondary particle diameter is lessthan about 1000 nm, preferably less than about 500 mm, more preferablyfrom about 2 nm to about 300 nm, even more preferably from about 2 nm toabout 200 nm and even more preferably from about 2 nm to about 100 nm.The primary particle size, of course, is the lower limit of thesecondary particle size for a particular collection of particles, sothat the average secondary particle size preferably is approximately theaverage primary particle size. For some particle dispersions, thesecondary particle size can be approximately the primary particle sizeindicating that the particles are well dispersed.

Once the dispersion is formed, the dispersion may eventually separatesuch that the particles collect on the bottom of the container withoutcontinued mechanical stirring or agitation. Stable dispersions haveparticles that do not separate out of the dispersion. Differentdispersions have different degrees of stability. The stability of adispersion depends on the properties of the particles, the othercompositions in the dispersion, the processing used to form thedispersion and the presence of stabilizing agents. Suitable stabilizingagents include, for example, surfactants. Preferably, dispersions arereasonably stable, such that the dispersions can be used withoutsignificant separation during the subsequent processing steps formingthe composites, although suitable processing to form the composite canbe used to ensure constant mixing or the like to prevent separation ofthe particle dispersion.

Formation of Composites

The linker compound and the polymer/monomer components can be added tothe liquid with the particle dispersion simultaneously or sequentially.The order of combining the various constituents can be selected toachieve the desired results. The conditions within the liquid preferablyare suitable for the bond formation with the linker and possibly otherbond formation involving the polymer/monomer constituents. Once thecomposite is formed, the liquid can be removed or solidified to leavebehind a structure formed from the composite.

The polymer/monomer composition can be formed into a solution/dispersionprior to addition to the inorganic particle dispersion, or thepolymer/monomer can be added as a solid to the particle dispersion. Inpreferred embodiments, the polymer/monomer compositions are soluble inthe liquid used to form the particle dispersion. If the polymer/monomeris not soluble/dispersible in the particle dispersion, either thepolymer/monomer solution or the particle dispersion is slowly added tothe other while mixing to effect the reaction. Whether or not thepolymer/monomer is first solubilized separate from the inorganicparticle dispersion may depend on the kinetics of the polymer/monomersoluble/dispersible and on the desired concentrations of the varioussolutions/dispersions. Similarly, bonding kinetics can influence theorder and details of the mixing procedures.

The linkers generally can be added to the particle dispersion, to apolymer/monomer solution or to a mixture of the inorganic particles andthe polymer/monomer. For self-polymerizing linkers, it is preferable toadd the linkers to the particle dispersion such that the linkers morelikely bond to the particle surface rather than self-condensing. Forexample, alkoxysilanes hydrolize to a form that self-polymerizes. Theorder and amount of adding the linker may influence the details of theresulting composite structure. In particular, the linker preferably iswell dispersed when reacted with the inorganic particles such that moreuniform bonding to the inorganic particles results.

In some embodiments, the reaction conditions and/or the presence of acatalyst or the like is needed to initiate the reaction of the linkerwith the inorganic particle and/or the polymer/monomer. In theseembodiments, the components can be mixed prior to the adjustment of thereaction conditions of the addition of a catalyst. Thus, a well mixedsolution/dispersion can be formed prior to the adjustment of thereaction conditions or addition of the catalyst to form a more uniformcomposite.

Processing and Self-Assembly

Following formation of the polymer/inorganic particle composite, thecomposite can be subjected to further processing. Herein forconvenience, the composite refers to the bonded inorganicparticle-linker-polymer/monomer structure whether in solution, adispersion, a coating or a solid form. For example, the properties ofthe solution/dispersion, such as concentration and solvent composition,containing the composite can be modified to facilitate the furtherprocessing, for storage of the composite and/or for convenience. Inpreferred embodiments, the composites subsequently are incorporated intoparticular structures or devices to take advantage of the properties ofthe composite, as described further below. To facilitate formation intolocalized devices, the polymer can be selected for self-organizationproperties that assist the self-assembly of the composite into alocalized structure. Self-assembled structures can be formed fromself-assembly with particles segregated to one or another phase of thepolymer within the composite, in which different polymer phases areidentifiable due to self-organization.

The solution/dispersion in which the composite is formed can be useddirectly in further processing. Alternatively, the composite can beremoved from the liquid or placed in a different liquid. The liquid ofthe solution/dispersion can be changed by dilution, i.e., the additionof a different liquid to solution/dispersion, by dialysis to replace theliquid if the composite has sufficient molecular weight to be retainedby dialysis tubing, or by removing the liquid andsolubilizing/dispersing the composite with the replacement liquid.Dialysis tubing with various pore sizes are commercially available. Tosubstitute liquids, a liquid mixture can be formed, and subsequently theoriginal liquid is removed by evaporation, which can be particularlyeffective if the liquids form an azeotrope. The polymer/inorganiccomposite can be removed from a liquid by evaporating the liquid, byseparating a dispersion of the complex by filtration or centrifugation,or by changing the properties, such as pH, liquid composition or ionicstrength, of the solution/dispersion to induce the settling of thecomplex from the liquid.

Generally, the composite can be processed using standard polymerprocessing techniques, including heat processing and solvent processingapproaches. For example, the polymer/inorganic particle composite can beformed into structures by compression molding, injection molding,extrusion and calendering. In other words, the composites can be formedinto free structures, such as sheets. Similarly, the composites can beformed into fibers or a layer on a fiber using techniques, such asextrusion or drawing a softened form of the composite.Solutions/dispersions can be formed into films/coatings by spin castingand similar methods. Coatings can be formed with various parametersincluding, for examples, thin coatings with thicknesses less than about1 micron.

In some embodiments, the composite is formed into localized structuresby self-assembly. The composition and/or structure of the composite canbe selected to encourage self-organization of the composite itself. Forexample, block copolymers can be used such that the different blocks ofthe polymer segregate, which is a standard property of many blockcopolymers. Suitable block copolymers include, for example,polystyrene-block-poly(methyl methacrylate),polystyrene-block-polyacrylamide, polysiloxane-block-polyacrylate andmixtures thereof. These block copolymers can be modified to includeappropriate functional groups to bond with the linkers. For example,polyacrylates can be hydrolyzed or partly hydrolyzed to form carboxylicacid groups, or acrylic acid moieties can be substituted for all or partof the acrylated during polymer formation if the acid groups do notinterfere with the polymerization. Alternatively, the ester groups inthe acrylates can be substituted with ester bonds to diols or amidebonds with diamines such that one of the functional groups remains forbonding with a linker. Block copolymers with other numbers of blocks andother types of polymer compositions can be used.

The inorganic particles can be associated with only one of the polymercompositions within the block such that the inorganic particles aresegregated together with that polymer composition within the segregationblock copolymer. For example, an AB di-block copolymer can includeinorganic particles only within block A. Segregation of the inorganicparticles can have functional advantages with respect to takingadvantage of the properties of the inorganic particles. Similarly,tethered inorganic particles may separate relative to the polymer byanalogy to different blocks of a block copolymer if the inorganicparticles and the corresponding polymers have different solvationproperties. In addition, the nanoparticles themselves can segregaterelative to the polymer to form a self-organized structure.

Other ordered copolymers include, for example, graft copolymers, combcopolymers, star-block copolymers, dendrimers, mixtures thereof and thelike. Ordered copolymers of all types can be considered a polymer blendin which the polymer constituents are chemically bonded to each other.Physical polymer blends may also be used and may also exhibitself-organization, as described in the examples below. Polymer blendsinvolve mixtures of chemically distinct polymers. The inorganicparticles may bond to only a subset of the polymer species, as describedabove for block copolymers. Physical polymer blends can exhibitself-organization similar to block copolymers. The presence of theinorganic particles can sufficiently modify the properties of thecomposite that the interaction of the polymer with inorganic particlesinteracts physically with the other polymer species differently than thenative polymer alone.

Regardless of the self-organization mechanism, some self-organizedcomposites involve nanoparticles aligned with periodicity in asuperstructure or super crystal structure. The particles may or may notbe crystalline themselves yet they will exhibit properties due to theordered structure of the particles. Photonic crystals make use of thesecrystal superstructures, as described further below.

The self-organization capabilities of the composites can be usedadvantageously in the formation of self-assembled structures on asubstrate surface. To bind the composite to the surface, the polymer canbe simply coated onto the surface or the composite can form chemicalbonds with the surface. For example, the polymer can include additionalfunctional groups that bond to one or more structures and/or one or morematerials on the surface. These additional functional groups can befunctional side groups selected to assist with the self-assemblyprocess.

Alternatively, the substrate surface can have compositions, a surfacelinker, that bond to the polymer and/or to the inorganic particles suchthat a composite is bonded to the surface through the polymer or theinorganic particles. For example, the substrate can include organiccompositions with one or more functional groups such as halogens, suchas Br, CN, SCOCH₃, SCN, COOMe, OH, COOH, SO₃, COOCF₃, olefinic sites,such as vinyl, amines, thiol, phosphonates and combinations thereof.Alternatively, the surface linker has functional groups that react withunreacted functional groups in the polymer. Appropriate functionalgroups in the surface linker to bond with the polymer are equivalent tothe functional groups in the composite linker to bond with the polymer.

In some embodiments involving self-assembly with nanoparticles, aportion of the substrate surface is provided with pores, which can beholes, depressions, cavities or the like. The pores can be in an orderedarray or a random arrangement. The size of the pores should be largerthan the size of the nanoparticles. Generally, the pores have a diameterless than a micron, although the preferred size of the pores and densityof the pores may depend on the particular desired properties of theresulting device.

To deposit the composites within the pores, the surface is contactedwith a dispersion of the composites. Then, for example, the dispersionis destabilized with respect to the composites, such that the compositestend to settle onto the surface and into the pores. The dispersion canbe destabilized by altering the pH, such as adjusting the pH toward theisoelectric point, by diluting surfactants or by adding a cosolvent thatresults in a less stabile dispersion. The dispersion is removed afterthe deposition of a desirable amount of composites. Then, composite onthe surface not in the pores can be removed. For example, the surfacecan be rinsed gently with a dispersant to remove composite on thesurface. Alternatively, the surface can be planarized by polishing, suchas mechanical polishing or chemical-mechanical polishing. If thedispersant is properly selected to be not be too effective at dispersingthe composite and if the rinsing is not done too extensively, thecomposite along the surface can be preferentially removed while leavingthe composite within the pores behind.

A porous structure can be formed using anodized aluminum oxide or othermetal oxides. Anodized aluminum oxide forms highly oriented and veryuniform pores. Pores are formed in anodic aluminum oxide by place analuminum anode in a solution of dilute acid, such as sulfuric acid,phosphoric acid, or oxalic acid. As the aluminum is oxidized, aluminumoxide with pores is formed. Pore diameters at least can be variedbetween 4 nm and 200 nm. The pores have a depth on a micron scale. Theformation of porous anodized aluminum oxide is described, for example,in D. Al-Mawlawi et al., “Nano-wires formed in anodic oxidenanotemplates,” J. Materials Research, 9: 1014-1018 (1994) and D.Al-Mawlawi et al., “Electrochemical fabrication of metal andsemiconductor nano-wire arrays,” in Proc. Symp. Nanostructured Mater.Electrochem., 187th Meeting Electrochem. Soc., Reno, Nev., May 21-26,1995, Electrochem. Soc. 95(8): 262-273 (1995). The use of blockco-polymers to form ordered array of pores from silica and filling thepores to form a photonic crystal is described in U.S. Pat. No. 6,139,626to Norris et al., entitled “Three Dimensionally Patterned Materials andMethods For Manufacturing Same Using Nanocrystals,” incorporated hereinby reference.

The formation of a plurality of devices on a surface requires thelocalization of compositions active in the devices within prescribedboundaries associated with the particular device. To localize astructure within prescribed boundaries by self-assembly, the overallprocedure generally requires both a process defining the boundaries ofthe structure and a separate self-assembly process using a chemicalaffinity to associate the compositions of the device within theboundaries. The boundary defining process generally utilizes externalforces to define the extent of the structures. The self-assembly processitself generally does not define the boundaries of the structure.Self-assembly is based on a natural sensing function of thecompositions/materials that results in a natural ordering within theresulting structure as the compositions/materials associate. In general,the localization step can be performed before or after the self-assemblyprocess, although the nature of the processing steps may dictate aparticular order. The net effect results in a self-assembled structurewith a corresponding coverage of polymer/inorganic particle compositewithin the boundary and an area outside of the boundary lacking thiscoverage.

The separate boundary defining process is coupled to the self-assemblyprocess by activating the self-assembly process within the boundaries orby deactivating the area outside of the boundaries. Generally, anoutside force is applied to perform the activation or deactivationprocess. The localization can be performed, for example, using a mask orthe like, or using maskless lithography with focused radiation, such asan electron beam, an ion beam or a light beam.

The identification of a suitable activation or deactivation techniquemay depend on the particular self-assembly approach used. Thelocalization approaches generally involve either activation of the areafor the placement of the self-assembled structure or by deactivatinglocations separate from the selected locations. In particular, thelocalization approach isolates the region for the formation of theself-assembled structure. Suitable physical forces or chemical materialsare applied to perform the activation/deactivation.

Various approaches can be adapted for these purposes, including, forexample, conventional integrated electronic circuit processingapproaches. Specifically, mask techniques can be used to isolate theboundaries of the activation/deactivation process. Radiation or chemicalapplication can be performed in regions defined by the mask. Similarly,focused beams can be used to perform the localization. Suitable focusedbeams to achieve surface modification include, for example, light beams,such as ultraviolet light or x-ray, laser beams, electron beams or ionbeams, which can be focused to impinge on the selected region to performactivation or deactivation. Suitable focusing approaches are known inthe art.

An activation process can involve the formation of a specific materialat the desired location or the removal of a material or composition thatis inhibiting self-assembly at the desired location. Specifically, aparticular material can be formed within the boundaries that allows forthe self-assembly process to occur within the boundaries, while thesurface material outside of the boundaries does not allow for theself-assembly process. For example, a chemically reactive layer can beformed within the boundaries that binds to a polymer, while thesubstrate surface outside the boundary has a different chemicalfunctionality that does not bind to the polymer. Similarly, a layer ofan inhibiting compound can be removed from the area within theboundaries to expose a surface material that binds to a compoundrequired in the self-assembly process, such as a surface linker. Theinhibiting compound can be a photoresist compound in some instances thatphysically blocks the surface and is selectively removable before orafter the self-assembly process. The composition of the photoresist orother inhibition compound is selected to inhibit the self-assemblyprocess such that the regions covered by the inhibitory compoundsurrounding the boundary region subsequently do not become involved inthe self-assembly process.

Similarly, the regions outside of the boundary region can bedeactivated. For example, a composition that binds a compound involvedin the self-assembly process can be applied over an entire surface.Then, the composition can be removed from outside of the bounded regionselected for the self-assembly process. Then, the self-assembly processonly takes place within the bounded region. In addition, an inhibitormaterial can be specifically deposited outside of the boundary region sothat the self-assembly process only takes place within the boundedregion where the inhibitory material has been removed. Similarly,radiation can be used to inactivate or dissociate compounds outside ofthe bounded region. The mask and/or focused beam approaches describedabove can be used to perform the deactivation processes. As noted above,strata or layers can be processed to produce a three dimensionalintegrated structure.

A localization process used along with self-assembly is describedfurther in copending and commonly assigned U.S. patent application Ser.No. 09/558,266 to Kambe et al., entitled “Self Assembled Structures,”incorporated herein by reference.

Uses of Composites

The polymer/inorganic particle composite materials are suitable for theefficient formation of devices incorporating a very wide range ofmaterials. The composites can incorporate preferably one or more of thevarious very uniform nanoparticles that have been described above.Selective incorporation of particular composites into a particulardevice can establish desired function for a device due to the choice ofcomposite.

In preferred embodiments, the structures form a microscopicconfiguration with two dimensional or three dimensional features thatare integrated to form a complete integrated article. The term“nanoscopic” is used to refer to structure within an individualself-assembled device. The resulting three dimensional structure forms asuperlattice or superstructure. Also, fibers formed using the compositescan be used, for example, as optical fibers or as electrical oropto-electronic devices.

Examples of structures placed along a substrate incorporatingpolymer/inorganic particle composites are shown in FIG. 10. Referring toFIG. 10, a substrate 200 includes structures or islands 202, 204, 206,208, 210, 212 with composite material. Integrated self assembledstructures are described further in copending and commonly assigned U.S.patent application Ser. No. 09/558,266 to Kambe et al., entitled “SelfAssembled Structures,” incorporated herein by reference. Each of thecomposites in structures 202, 204, 206, 208, 210, 212 can include thesame composition or a different polymer composition and/or inorganicparticles as the other structures. Preferred nanoscale particles have anarrow particle size distribution of primary particles, such as thenanoparticles described above formed by laser pyrolysis. Similarly,preferred nanoscale particles have a small average secondary particlesize, generally resulting from the use of a preferred particledispersion.

Suitable devices incorporating nanoparticles or other self-assembledcompositions include, for example, energy sources, such as batteries;photonic crystals; active electrical or electro-optical elements, suchas field emission devices; and passive elements, such as electricalinterconnects, barrier layers and insulating layers. Electrodes can beformed with self-assembled electroactive particles along withelectrically conductive particles. Similarly, the electrodes can beformed with electrically conducting polymers and suitable inorganicparticles to form the composite.

Photonic crystals are ordered arrays of composite composition having aunit cell size of the photonic crystal ranging from about one quarter toabout one optical wavelength. The index-of-refraction of the materialdepends on the wavelength of light. For example, visible light in airhas a wavelength of about 380 nm to about 780 nm. Generally, photoniccrystals of interest have size from about 100 nm to about 1000 nm. Theparticles form a crystal superstructure with alternating regions ofindex-of-refraction. The photonic crystals can be formed from an orderedarray of nanoparticles of, for example, metals, silica, silicon nitride,silicon oxynitride, titania or zinc oxide. Due to the size of theordered arrays, the photonic crystals can have a photonic band gap thatprevents propagation of light in any direction. Thus, photonic crystalscan be used for control of spontaneous emission and for very sharpbending of light. Self-assembly, as described above, can be used to formthe ordered arrays.

Electrical interconnects can be constructed from electrically conductiveparticles, for example, metal nanoparticles, such as silver and goldnanoparticles. Similarly, optical interconnects provide for transmissionof light between devices. Integrated optical interconnects can be formedfrom materials with suitable indices of refraction. For transmittingvisible light, silica, alumina and zinc oxide, for example, can be used.Barrier layers can be formed, for example, from silicon oxide particlesunder higher index-of-refraction materials. Insulating layers can beformed, for example, from silicon dioxide nanoparticles. Field emissiondevices for displays can incorporate phosphor particles, such as zincoxide or doped zinc oxide.

Referring to FIG. 11, a coupler/divider is shown. Coupler/divider 250includes a coupled arm 252 and two branches 254. Coupler/divider 250 canbe used to connect a plurality of devices by electrical transmission orfor optical transmission. Suitable materials for electrical and opticaltransmission are described above.

Referring to FIGS. 12 and 13, a field effect transistor (FET) is shown.FET 300 includes a source electrode 302, a drain electrode 304, achannel 306 and a gate electrode 308. One or more of the elements can beconstructed using self-assembled materials using the approachesdescribed herein. In particular, electrodes 302, 304, 308 can be formedusing electrically conductive metals, as described above. Channel 306can be formed from an electrically insulating material.

In particular, the use of polymer/inorganic particle composites isparticularly useful for the formation of devices with a selecteddielectric constant/index-of-refraction. Through index-of-refractionengineering, the materials can be designed specifically for a particularapplication. Appropriate selection of index-of-refraction can beimportant for the preparation of either electrical or optical materials.The index-of-refraction is approximately the square root of thedielectric constant when there is no optical loss, so that theengineering of the index-of-refraction corresponds to the engineering ofthe dielectric constant. Thus, the index-of-refraction/dielectricconstant is related to both the optical and electrical response of aparticular material. Index-of-refraction engineering can be especiallyadvantageous in the design of optical or electrical interconnects.

For optical materials, the transmission of light and optical propertiesat interfaces depend directly on the selection of an appropriateindex-of-refraction. In particular, the refractive and reflectiveoptical properties of a material are directly related to theindex-of-refraction. For example, high index-of-refraction materials canbe used to form microlenses that focus light due to bending of light atinterfaces with lower index materials. These lenses can be called gradedindex lenses. The angle of the bending of light can be expressedaccording to Snell's law, n₁ sin È₁=n₂ Sin È₂, where n₁ and n₂ are theindices of refraction in the respective materials 1 and 2 and È₁ and È₂are the respective angles. The imaginary portion of the complexindex-of-refraction is related to the absorption of light.

In addition, the electrical properties of a material can also depend onthe dielectric constant. For example, the capacitance of a material isdirectly proportional to the dielectric constant of the material. Toreduce the capacitance of an electrical interconnect within anintegrated circuit, it is desirable to have a low dielectric constant,preferably less than 2. Thus, low K materials are desired forfabrication into integrated circuits.

In addition, the time constant for electrical response of a material isrelated to the dielectric constant. In response to an electric field, aconducting medium generally approaches electrostatic equilibrium with arate proportional to e^(−gt/K), where t is time, g is a constant and Kis the dielectric constant. Thus, if K is larger, the conductorapproaches equilibrium more slowly. In a field effect transistor, it isdesirable to have a high K material adjacent the channel. In theembodiment shown in FIGS. 12 and 13, the channel 306 connects sourceelectrode 302 and drain electrode 308. The use of high K materialadjacent the channel reduces current leakage.

Since laser pyrolysis is a flexible method for the synthesis of a widerange of inorganic particles/powders, these particles can be selected tohave a desired dielectric constant. Specifically, TiO₂ generally has ahigh index-of-refraction with values ranging from about 2.5 to about2.9. SiO₂ generally has a relatively low index-of-refraction from about1.45 to about 1.5. Polymers generally have a low index of refractionfrom about 1.3 to about 1.6. The high index-of-refraction compositespreferably have an index-of-refraction of at least about 1.8. The lowindex-of-refraction composites preferably have an index-of-refraction ofno more than about 1.5.

EXAMPLES Example 1 Formation of Titanium Oxide Particles

Rutile TiO₂, anatase TiO₂, and oxygen deficient blue TiO₂ particles wereproduced by laser pyrolysis. The reaction was carried out in a chambercomparable to the chamber shown in FIGS. 14-16.

Referring to FIGS. 14-16, a pyrolysis reaction system 400 includesreaction chamber 402, a particle collection system 404 and laser 406.Reaction chamber 402 includes reactant inlet 414 at the bottom ofreaction chamber 402 where reactant delivery system 408 connects withreaction chamber 402. In this embodiment, the reactants are deliveredfrom the bottom of the reaction chamber while the products are collectedfrom the top of the reaction chamber.

Shielding gas conduits 416 are located on the front and back of reactantinlet 414. Inert gas is delivered to shielding gas conduits 416 throughports 418. The shielding gas conduits direct shielding gas along thewalls of reaction chamber 402 to inhibit association of reactant gasesor products with the walls.

Reaction chamber 402 is elongated along one dimension denoted in FIG. 14by “w”. A laser beam path 420 enters the reaction chamber through awindow 422 displaced along a tube 424 from the main chamber 426 andtraverses the elongated direction of reaction chamber 402. The laserbeam passes through tube 428 and exits window 430. In one preferredembodiment, tubes 424 and 428 displace windows 422 and 430 about 11inches from the main chamber. The laser beam terminates at beam dump432. In operation, the laser beam intersects a reactant stream generatedthrough reactant inlet 414.

The top of main chamber 426 opens into particle collection system 404.Particle collection system 404 includes outlet duct 434 connected to thetop of main chamber 426 to receive the flow from main chamber 426.Outlet duct 434 carries the product particles out of the plane of thereactant stream to a cylindrical filter 436. Filter 436 has a cap 438 onone end. The other end of filter 436 is fastened to disc 440. Vent 442is secured to the center of disc 440 to provide access to the center offilter 436. Vent 442 is attached by way of ducts to a pump. Thus,product particles are trapped on filter 436 by the flow from thereaction chamber 402 to the pump.

Titanium tetrachloride (Strem Chemical, Inc., Newburyport, Mass.)precursor vapor was carried into the reaction chamber by bubbling Ar gasthrough TiCl₄ liquid in a container at room temperature. C₂H₄ gas wasused as a laser absorbing gas, and argon was used as an inert gas. O₂was used as the oxygen source. Additional argon was added as an inertdiluent gas. The reactant gas mixture containing TiCl₄, Ar, O₂ and C₂H₄was introduced into the reactant gas nozzle for injection into thereactant chamber.

Representative reaction conditions for the production of rutile TiO₂particles and anatase TiO₂ particles are described in Table 1. Theblue-oxygen deficient rutile TiO₂ (TiO₂-2) was obtained from the sameconditions as the rutile TiO₂ particles (TiO₂-1) in Table 1, except thatthey were collected closer to the reaction zone by positioning theparticle collector accordingly. Low chamber pressure and low partialpressure of oxygen contribute to the oxygen deficiency in the resultingTiO₂. Heating of the particles slightly in air results in the loss ofblue color and the formation of a rutile structure. TABLE 1 TiO₂-3TiO₂-1 Anatase Phase Rutile TiO₂ TiO₂ BET Surface Area 64 57 (m²/g)Pressure (Torr) 110 150 Ar-Dilution Gas (slm) 4.2 8.4 Ar-Win (slm) 10.010.0 Ar-Sld. (slm) 2.8 2.8 Ethylene (slm) 1.62 1.25 Carrier Gas - Ar(slm) 0.72 0.72 Oxygen (slm) 2.44 4.5 Laser Power-Input 1400 1507(Watts) Laser Power-Out 1230 1350 (watts)sccm = standard cubic centimeters per minuteslm = standard liters per minuteArgon-Win. = argon flow through inlets 490, 492Argon-Sld. = argon flow through slots 554, 556

An x-ray diffractogram of product nanoparticles produced under theconditions in Table 1 are shown in FIG. 17. Sample TiO₂-1 had an x-raydiffractogram corresponding to rutile TiO₂. Sample TiO₂-2 had an x-raydiffractogram similar to sample TiO₂-1. Sample TiO₂-3 had an x-raydiffractogram corresponding to anatase TiO₂. The broadness of the peaksin FIG. 17 indicates that sample 1 is less crystalline than the othertwo samples. Some peaks in the spectra of sample TiO₂-1 seem tooriginate from amorphous phases.

Example 2 Formation of Particle Suspensions

This example provides a description of the formation of well disperseddilute solutions of titanium oxide nanoparticles produced by laserpyrolysis, as described in Example 1.

The suspensions were formed using each of the three types of TiO₂particles described in Example 1. The three powders were separatelysuspended in water, ethanol, dimethyl sulfoxide (DMSO), cyclohexane,cyclohexanone and phentydrone (1,2,3,4-tetrahydro-9-fluorenone, THF).The suspensions were formed with 9.75 milligrams (mg) of TiO₂ powders in13 grams of liquid resulting in a suspension with 0.075 wt % TiO₂. Thesamples were sonicated for 2 hours each in a sonicate bath. Then, therelative sedimentation of all the samples was visually detected inparallel for two weeks.

The results are presented in Table 2. The relative sedimentation of allthe samples is marked in parentheses following observations after twoweeks and then several months, with number 1 being the worst and number7 being the best. TABLE 2 Solvent TiO₂-1 TiO₂-2 TiO₂-3 water very poor(3) very poor (1) very poor (2) 100% settled 100% settled  100% settledcyclohexanone very good (4) very good (5) excellent (7) ˜90% suspended˜85% suspended ˜100% suspended cyclohexane very poor (2) very poor (2)very poor (3) 100% settled 100% settled  100% settled ethanol excellent(6) good (4) excellent (6) ˜95% suspended >75% settled  ˜90% suspendedTHF excellent (5) excellent (7) very poor (4) ˜95% suspended >30%settled* ˜100% settled DMSO very good (7) very good (6) poor (5) ˜80%suspended* >50% settled*  >70% settled toluene very poor (1) very poor(3) very poor (1) 100% settled 100% settled  100% settled*The suspended particles remained suspended for months.

The best suspensions for a short term period (i.e., minimumsedimentation is observed after two weeks) were formed withcyclohexanone and ethanol. THF also suspended one of the samplesextremely well. These suspensions exhibited no or only slight depositionof particles even after two weeks. A graph of relative ranking, afterobservations after two weeks, as a function of dielectric constant (K)is shown in FIG. 18. This plot suggests that solvents/dispersants withmedium polarity provide the best suspensions, while solvents with verylow or very high dielectric constant are not as suitable.

Secondary particle size in the suspensions were evaluated with a HoribaParticle Size Analyzer (Horiba, Kyoto, Japan). Analysis with theparticle size analyzer showed good dispersion/low agglomeration with alldispersants that suspended well the particles. Generally, all of thesuspended particles were in the size region below 80 nm, with broaderdistributions with lower average particle size.

Since the particle size analyzer had a detection cut-off at 30 nm, aninternal standard was used to estimate the number of particles withdiameters less than 30 nm. A well characterized commercial TiO₂ powder(R706 average particle size 0.36 microns with a coating of Al₂O₃,DuPont, Wilmington, Del.) was mixed with the nanoparticles in a 1 to 1by weight ratio. The resulting suspension was analyzed with the Horibaparticle size analyzer. Less than about 10 percent of the nanoparticleswere observed. Thus, most of the nanoparticles had a diameter less thanabout 30 nm and are undetected by the particle size analyzer.Nevertheless, the trends measured with the particle size analyzer wereindicative of the level of agglomeration. In particular, gooddispersions were formed with solvents that performed well in suspendingthe particles.

Absorption spectra were obtained for titanium oxide particles in ethanolat a concentration of 0.003 weight percent. The spectra for TiO₂-1,TiO₂-2 and TiO₃-3 samples are shown in FIGS. 19-21, respectively. Forcomparison, similar spectra were obtained for two commercial TiO₂powders dispersed in ethanol at a concentration of 0.0003 weightpercent, which are shown in FIGS. 22 and 23. The first commercial powder(FIG. 22) was obtained from Alfa Aesar, Inc., Ward Hill, Mass. and hadan average particle size of 0.17 microns. The second commercial powder(FIG. 23) was obtained from Aldrich Chemical Company, Milwaukee, Wis.,and had an average particle size of 0.26 microns.

The absorption spectra of the TiO₂ in FIG. 23 is exemplary of bulk TiO₂with a large absorption in the visible and infrared portions of thespectra. In contrast, the absorption spectra of the powders in FIGS.19-22 have very reduced absorption in the visible and infrared portionsof the spectra and enhanced absorption in the ultraviolet. This shiftand narrowing of the absorption spectra is due to the reduced size ofthe particles. The spectra of the laser pyrolysis materials in FIGS.19-21 have an even more reduced visible absorption and a narrower andenhanced ultraviolet absorption relative to the powders yielding thespectrum in FIG. 22.

Example 3 Surface Treatment of Titanium Oxide Particles

Surface treatment of the three types of TiO₂ particles was performedwith aminopropyl triethoxy silane (APTES) as a silylation reagent. APTESis thought to bond to the particles by the following reaction:Particle-Ti—OH+((CH₃CH₂O)₃—SiCH₂CH₂CH₂NH₂→Particle-Ti—O—Si(OCH₂CH₃)₂CH₂CH₂CH₂NH₂Further successive hydrolysis of the ethoxy groups can form additionalSi bonds to the particle through ether-type linkages. Someself-polymerization of the silylation reagent can take place also,especially if excess silylation reagent and water are present.

Based on the measured BET surface areas of the particles, the quantityof APTES ½, 1 and 2 of the particle surface relative to a monolayer ofthe linker was calculated. Excess silylation reagent can be addedbecause not all of the silylation reagent binds and someself-polymerization of the silylation reagent can take place. Tocalculate the coverage, the APTES was assumed to bond to the particlenormal to the surface. Then, an estimate was made on the size of themolecule. This calculation only provides a rough estimate of thecoverage. As described below, it was found experimentally that highercoverage could be placed over the surface of the particles thanestimated from these calculations.

An experiment was performed to examine the coating of the particles. Asdescribed in the following examples, these silylated particles weresubsequently used to form polymer composites. In forming thesecomposites, a polymer was reacted with the coated particles withoutremoving them from solution. Ethanol was used as the solvent since onepolymer of interest, polyacrylic acid, is more soluble in ethanol thancyclohexanone. In addition, ethanol absorbs moisture better, andmoisture was needed to assist with hydrolysis of the ethoxy groups.

To prepare the silylated particles, APTES solutions were prepared infresh ethanol having traces of water with quantities suitable for 50%coverage, 100% coverage and 200% coverage. Additional reagent was usedbased on the assumption that some reagent will be left in solution andthat the calculated coverage values are only rough estimates. Vials with100 mg of TiO₂-3 and 4 g of solution were prepared outside the dry boxto allow moisture uptake. However, extended exposure to water wasavoided, and the vials were sealed after solvent addition. The sealedvials were sonicated and then left for about 72 hours.

The powders settled on the bottom of the vials. The supernatant clearsolution, i.e., the solution above the settled particles, was removedwith a pipette, and fresh ethanol was added. Then, the powders suspendedwell. The supernatant was found to contain unreacted silylation agent.In the samples prepared with estimated amounts of APTES sufficient for50% coverage, 100% coverage and 200% coverage, the percent of originalAPTES that was removed with the supernatant solutions were 44.7%, 28.7%and 32.4%, respectively. Thus, the calculated estimates appear to be lowin terms of the coverage of APTES on the particles since more than 100%coverage was obtained when the initial solution had the estimated amountfor 200% coverage and less than 50% was recovered.

The interaction with the suspended silylated particles with polyacrylicacid is described in the following Example.

Example 4 Formation of Poly(Acrylic Acid)/Titanium Oxide ParticleComposites

The formation of composites with poly(acrylic acid) and TiO₂-3 powderswith silane based linkers is described in this example. The wellsuspended APTES coated TiO₂-3 particles described in Example 3 were usedin these studies.

The polyacrylic acid is thought to react with by way of the carboxylicacid group with the primary amine of the silylation agent to form anamide bond. The first interaction of the polymer with the surfacetreated particles involves the salt formation of the carboxylic acidwith the primary amine. Then, at temperatures of 140°-160° the saltunits condense to form amide bonds. This reaction is depictedschematically as follows:Polymer-COOH+H₂N— . . . —Si—O—Ti-particle—Polymer-CONH— . . . .Si—O—Ti-particle.

A fourier transform infrared spectrum of the composite had an infraredabsorption band at 1664 cm⁻¹, which is a frequency characteristic of anamide bond. This infrared absorption spectrum for a composite formedwith 2000MW polymer and twice a monolayer quantity of TiO₂-3 particle isshown in FIG. 24 with label A. A corresponding spectrum of a compositeformed with unmodified particles is shown in FIG. 24, labeled B. Theinfrared absorption spectrum for the polymer without any titanium oxideparticles is shown in FIG. 24, labeled C. The spectra labeled B and C inFIG. 24 lack the amide absorption band.

The spectrum labeled A in FIG. 24 involves a composite treated at 160°C. after combining the constituents. This spectrum is also shown in FIG.25, labeled A. The spectrum of the composite treated at 120° C., labeledB in FIG. 25, shows less pronounced amide bond formation. The spectrumof a composite treated at 230° C., labeled C in FIG. 25, shows aincrease of amide bond structure.

Composites were formed with two different polymer molecular weights andwith two different particle loadings. Poly(acrylic acid)(PAA) was alsoadded to a dispersion of particles that was not modified with thesilylation agent. The suspended treated particles were separated intoequal samples to form the different composites. Higher particle loadingsamples were produced with 1 equivalent by weight of PAA per titaniumoxide particles to produce composites with 50% by weight particles.Lower particle loading samples were produced with 9 equivalents byweight of PAA per titanium oxide particles to produce composites with10% by weight particles. The low molecular weight polymer had an averagemolecular weight of 2,000 Daltons, and the high molecular weight polymerhad an average molecular weight of 250,000 Daltons. Thus, a total offour types of samples were produced with functionalized TiO₂-3particles, and four control samples were produced with untreated TiO₂-3particles.

Upon applying the composites as a coating, dramatic differences werevisible in the microstructure between the samples formed with treatedparticles and those formed with untreated particles. The coatings wereformed by placing drops on a surface. The drops spread on the surfaceand were allowed to dry. The dried composites were further analyzed. Inparticular, much smoother materials were formed from the functionalizedparticles than with the unfunctionalized particles. Similarly,significant differences were observed between samples produced with thehigh molecular weight polymer and the low molecular weight polymer. Thelower molecular weight polymer resulted in smoother materials.

Scanning electron micrographs (SEM) were obtained for coatings formedwith composites having silylated particles and with untreated particles.SEM photos for silylated, i.e., treated, and untreated particles with aten percent particle loading with 2000MW polymer at two magnificationsare shown in FIGS. 26-29. The composites with the treated particles(FIGS. 26 and 27) appear to form a smooth and more homogenous materialthan the composites formed with the untreated particles (FIGS. 28 and29). Similarly, SEM photos for composites with treated and untreatedparticles at a particle loading of 50 weight percent at twomagnifications are shown in FIGS. 30-33. Coatings with the treatedparticles (FIGS. 30 and 31) form a smooth and homogenous coating whilethe composites with the untreated particles (FIGS. 32 and 33) exhibitagglomeration and a rough surface.

Comparable photos were obtained for composites formed with polymerhaving a molecular weight of 250,000 Daltons. SEM photos for compositeswith a 10 weight percent loading of particles at two magnifications areshown in FIGS. 34-37. Less agglomeration is observed with the treatedparticles (FIGS. 34 and 35) than with the composites including theuntreated particles (FIGS. 36 and 37). SEM photos for composites with a50 weight percent loading are shown in FIGS. 38-41. Again, thecomposites formed with treated particles (FIGS. 38 and 39) form filmsthat are more uniform and less agglomerated than the composites formedwith untreated particles (FIGS. 40 and 41).

Differential scanning calorimetry was used to examine for thermalstability of the composites. The samples were first dried at 60° C.under high vacuum. The results are plotted in FIG. 42 for (1) 50%loading of TiO₂ modified with silane linkers and PAA (2000MW), (2) 50%loading of TiO₂ unmodified and PAA (2000MW), (3) PAA (2000MW) solidifiedfrom ethanol and (4) PAA (2000MW) from the manufacturer. The compositesformed from the functionalized particles exhibited significantly higherthermal stability.

Example 5 Evidence for Possible Self-Organization with Addition ofPolyethylene Glycol

The composite formed with silylation functionalized TiO₂ particles andPAA described in Example 4 were further mixed with polyethylene glycolto examine the resulting structure.

The TiO₂-PAA composites of Examiner 4 with 50% (1:1) TiO₂ loading in PAA(2000MW) were blended with polyethylene glycol (PEG) in ethanol. Theblend included 90 weight percent PEG and 10% weight percent TiO₂-PAAcomposite. The PEG-TiO₂-PAA composites were formed into coating bydripping the composite onto to surface and drying the material.Alternatively, the composites were cast into a film. Equivalent resultswere obtained by the two approaches. For comparison, a polymer blendwith no TiO₂ particles at all were formed. These polymer blends formed asticky surface and did not form a smooth surface.

When untreated TiO₂ particles were used to form the composite, theresulting mixture after adding the PEG had homogenous dispersedparticles within the polymer film. Some random grains were visuallyobservable and slight stripping could be seen. However, when thecomposite with the silylation functionalized particles were used, therewas segregation into domains. Specifically, a pronounced stripe patterncould be seen. The organization into a geometric pattern provides directevidence of self-organization.

Example 6 Composites with Polyamides

This example involves the formation of titanium oxide/nylon composites.These composites were formed by reacting silylated titanium oxideparticles with 6-amino-caproic acid. This example demonstrates theformation of a composite simultaneously with polymerization of theorganic species.

6-amino-caproic acid can self-polymerize to form a polyamide. Followingthe self-polymerization, a coating of the resulting polyamide forms asmall, precise feather-like pattern. The corresponding SEM micrographfor the polymer without any titanium oxide particles is shown in FIGS.43 and 44 at two magnifications. If untreated particles were used areused to form a composite with the polyamide, the particles segregatedwithin the polymer and did not form a homogenous composite. This isclearly visible in an SEM photographs in FIGS. 45 and 46, at twomagnifications. The underlying structure of this material forms apattern similar to the polyamide polymer alone. However, if thecomposite was formed with treated, i.e., silylated, TiO₂-3 particles,the composite formed a crystallization pattern different from thecrystallization pattern formed by the polymer alone. Specifically, thecomposite formed a pattern with longer range order, multiple branchingand ordering on different range scales. For a composite with a 50 weightpercent particle loading, SEM photographs are shown in FIGS. 47-48 attwo magnifications that demonstrate the incorporation of the particlesinto a highly ordered structure.

Example 7 Composites with Adipic Acid

This example demonstrates the formation of a composite formed frommonomer units. In this case, the monomers are not polymerizedthemselves. The monomers interact with the functionalized TiO₂ particlesto form a polymer in which the particles themselves form a star linkageswithin the overall polymer structure.

The monomer unit is adipic acid, HOOC(CH₂)₆COOH. The adipic acid canbond to the primary amine of the silylation agent with each carboxylicacid functional group. Thus, a polymer in a network is formed with theadipic acid and the silylated particles functioning as monomer units inthe ultimate polymer. Fourier transform infrared measurements provideevidence of amide bond formation when the adipic acid is reacted withthe functionalized particles. The infrared spectrum of the compositewith silylated particles (A) with an amide bond and untreated particles(B) are shown in FIG. 49.

In the resulting TiO₂-polymer composite formed with untreated TiO₂particles forms a homogeneous coating without patterns. In the compositeformed with silylated TiO₂ particles, there is visible agglomeration ofthe particles to form a single band that is clearly visible uponinspection.

The embodiments described above are intended to be illustrative and notlimiting. Additional embodiments are within the claims. Although thepresent invention has been described with reference to preferredembodiments, workers skilled in the art will recognize that changes maybe made in form and detail without departing from the spirit and scopeof the invention.

1. A structure comprising a surface and a composite localized withinboundaries on the surface, the composite comprising inorganic particlesbonded to a polymer.
 2. The structure of claim 1 wherein the structureis a fiber.
 3. The structure of claim 1 wherein the inorganic particleshave an average particle size less than about 100 nm.
 4. The structureof claim 1 wherein the inorganic particles have an average particle sizeless than about 50 nm.
 5. The structure of claim 1 wherein effectivelyno inorganic particles have a diameter greater than about 4 times theaverage diameter.
 6. The structure of claim 1 wherein at least about 95percent of the particles have a diameter greater than about 40 percentof the average diameter and less than about 160 percent of the averagediameter.
 7. The structure of claim 1 wherein the structure comprises anoptical device.
 8. The structure of claim 7 wherein the composite has anindex-of-refraction at least about 1.8.
 9. The structure of claim 7wherein the composite has an index-of-refraction of no more than about1.5.
 10. The structure of claim 7 wherein the optical device comprises aphotonic crystal.
 11. The structure of claim 1 wherein the compositecomprises at least about 5 weight percent of the inorganic particles.12. The structure of claim 1 wherein the composite comprises at leastabout 25 weight percent inorganic particles.
 13. The structure of claim1 wherein the composite is a film on the substrate.
 14. The structure ofclaim 1 wherein the composite is a self-assembled material.
 15. A fieldemission device comprising a structure of claim
 1. 16. A field effecttransistor comprising a structure of claim
 1. 17. A method for forming adevice on a solid substrate, the method comprising associating acomposite with the solid substrate, the composite comprising a polymerchemically bonded with an inorganic particle, wherein the composite islocalized into a specific region on the solid substrate surface.
 18. Themethod of claim 17 wherein the inorganic particles comprisemetal/metalloid particles, metal/metalloid oxides, metal/metalloidnitrides, metal/metalloid carbides, metal/metalloid sulfides,metal/metalloid phosphates or mixtures thereof.
 19. The method of claim17 wherein the polymer comprises polyamides, polyimides, polyacrylates,poly acrylic acid, polyacrylamides, polysiloxanes or mixtures thereof.20. The method of claim 18 wherein the polymer comprises polymers withconjugates polymer backbones, polymers with aromatic polymer backbones,or mixtures thereof.
 21. The method of claim 18 wherein the polymercomprises electrically conducting polymers.
 22. The method of claim 18wherein the composite has at least about 25 weight percent inorganicparticles.
 23. The method of claim 18 wherein the association of thecomposite comprises a self-assembly process.
 24. The method of claim 23wherein the association of the composite further comprises a boundarydefining process.